Observing Programmes: Interstellar Medium and Star Formation

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Guaranteed Time (Key Programmes)


Evolution of Interstellar Dust

The scientific motivation for this proposal is to trace the evolution of dust grains in relation to changes of the physical, dynamical and chemical properties of the interstellar medium. This program will provide an unprecedented view of the structure of the interstellar medium (ISM)  at far-infrared and submillimeter wavelengths and will enable us to investigate the impact of dust grains on the ISM's physical and chemical state. The program will take full advantage of four unique characteristics of SPIRE and PACS: sensitivity, wavelength coverage, angular resolution, and mapping efficiency. The brightness sensitivity is essential to measure the faint infrared emission from the diffuse regions. The spectrometers will provide the necessary information to derive the physical properties of the atomic and molecular gas and completely characterize dust evolution. The angular resolution is critical for tracing the dominant processes in grain evolution which takes place on all scales down to a few arcseconds. The data statistics will allow us to probe the impact of extreme physical conditions, e.g., high densities, intense vortices or illumination, on the dust evolution. Our goal is to build with Herschel a coherent database on interstellar dust emission extending to much smaller angular scales than the IRAS and DIRBE surveys and covering a wide range of ISM physical conditions, from diffuse clouds to the sites of star formation and protostars.

Lead Scientists: Alain Abergel (Institut d'Astrophysique Spatiale (IAS)), Annie Zavagno (Laboratoire d'Astrophysique de Marseille (LAM))

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CHESS: Chemical Herschel Surveys of Star forming regions

Study of the molecular content of regions far beyond our Solar System has advanced enormously during the last few decades, from the first detections of diatomic molecules to the discovery of polyatomic, complex organic molecules. Nowadays, one major goal of Astrochemistry is to have the most accurate census of the molecular content (and complexity) in Star Forming Regions (SFRs). It is in the frequency range covered by HIFI that light molecules emit in cold gas, while heavier molecules emit light when in warm gas. The latter are excited in the warm gas, whereas the former probe the gas at low temperatures as well. We will to obtain Spectral Surveys of a representative sample of SFRs, providing a large dataset of uttermost interest for the entire astronomical community, and, particularly for the study of star formation processes and of the influence of chemistry on star and planet formation.

Click here to go to the CHESS website.

Lead Scientist: Cecilia Ceccarelli (Laboratoire d'Astrophysique de Grenoble)

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HEXOS: Herschel Observations of Extraordinary Sources

HEXOS will use the HIFI and PACS instruments to perform full spectral line surveys of 5 sources in the Orion and Sagittarius B2 molecular clouds. These two sources contain the best-studied examples of physical and chemical processes that are prevalent in the interstellar space and associated with the birth of massive stars and stellar clusters. This includes exploring the physical and chemical conditions that exist in gas in close proximity to massive stars that is heating and exposed to energetic dynamical events caused by the tremendous release of energy by the star. In addition, we will be sensitive to ambient gas that is directly exposed to radiation from previous generations of star formation. Herschel offers unprecedented sensitivity and near continuous spectral coverage across the gaps imposed by the atmosphere.

Click here to go to the HEXOS website.

Lead Scientist: Edwin Bergin (University of Michigan)

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WISH: Water in Star Forming Regions with Herschel

Water is one of the most abundant and important molecules in star-forming regions. In warm gas created by the presence of newly-formed stars, water can become the third most abundant species. This includes the inner protostellar envelopes where the dust is warmer than the ice evaporation temperature, and the regions where the collapsing matter interacts with the powerful jets from the protostar causing violent shocks. This enormous variation in abundance makes water a unique probe of the physical structure of the region, and of the fundamental chemical processes within the gas and between the gas and the grains.  WISH will conduct a comprehensive set of water observations towards a large sample of protostars, covering a wide range of masses and luminosities -from the lowest to the highest mass protostars-, and a large range of evolutionary stages -from the first stages represented by the pre-stellar cores to the last stages represented by the pre-main sequence stars surrounded only by their protostellar disks.

Click here to go to the WISH website.

Lead Scientist: Ewine van Dishoeck (Sterrewacht Leiden)

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 HOBYS: the Herschel imaging survey of OB Young Stellar objects

With its unprecedented spatial resolution in the critical 75-500 microns wavelength range, Herschel will provide a unique opportunity to determine, for the first time, the fundamental properties of the precursors of massive OB stars at distances out to a few thousand lightyears. The imaging speed of SPIRE and PACS in the parallel mode will enable us to map the entire extent of massive cloud complexes and detect the massive young stellar objects which have been overlooked by previous missions.  HOBYS will yield for the first time accurate far-infrared photometry, and thus good luminosity and mass estimates, for a comprehensive, homogeneous sample of OB-type young stellar objects at all evolutionary stages. The multi-wavelength imaging will also reveal spatial variations of the cloud temperature close to HII regions and OB associations. These data, along with the detailed photometric and spectroscopic study of a few prototypical regions of induced star formation, will allow us to determine the importance of external triggers for high-mass star formation in the nearest massive molecular cloud complexes.

Click here to go to the HOBYS website.

Lead Scientist: Frédérique Motte (SAp/CEA Saclay)
UK contact: Derek Ward-Thompson (Cardiff University)

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PRISMAS: Probing Interstellar Molecules with Absorption Line Studies

PRISMAS is dedicated to the detection and study of key molecules which are not accessible from the ground at FIR/submillimeter wavelengths (low atmospheric transmission), but which bear essential information on the physical and chemical processes ruling the interstellar medium (ISM), and especially on the growth of complex molecules. With its high spectroscopic and spatial resolution as well as with its high sensitivity, Herschel presents a unique opportunity to study these molecules that have been looked over with previous space missions.  PRISMAS will study many molecular species, such as hydrides and carbonaceous agregates. Hydrides contain Hydrogen plus one of the elements Deuterium, Carbon, Nitrogen, Oxygen, Fluorine and Chlorine. Eight sources within our Galaxy are identified as targets, and are mainly massive star forming regions surrounded by dust grains responsible for a strong continuum emission in the wavelength range studied here. Most of these sources are distant and have many interstellar clouds along their line of sight.

Click here to go to the PRISMAS website.

Lead Scientist: Maryvonne Gerin (CNRS Observatoire de Paris and École Normale Supérieure)

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The ealiest phases of star formation: from low- to high-mass objects

Present-day star formation starts in the coldest and densest cores of molecular clouds. Still, our knowledge about the very early stages of star formation is limited. Objects at these stages emit most of their luminosity at far-infrared wavelengths, which is not observable from the ground, hence our view in this wavelength range to date remains fuzzy at best.  The limited resolution of previous space missions means that the individual sources blend together, especially within protoclusters where the density of potential protostars is very high. In addition, it has severely hampered progress in characterising young and cold high-mass cores which are, on average, far more distant. Detailed knowledge about these pre- and protostellar stages is indispensable for answering fundamental questions about the physics of the early collapse phase, the core fragmentation and the general ways to finally form stars of all masses. With Herschel we have the unique opportunity to deeply scrutinise such cold cradles of stars with unprecedented sensitivity and angular resolution in the far-infrared. Using SPIRE and PACS this project will perform deep and directed mapping of confined regions, producing a unique sample of low and high-mass objects that have been identified as very promising sources for the study of initial conditions of star formation. The Herschel data will allow us to reconstruct the 3D density and temperature structure, and for the first time enable us to perform an advanced modelling of such cold cores that is not affected by simplifications and parameter ambiguities.

Lead Scientist: Oliver Krause (Max Planck Institut fuer Astronomie)

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Gould Belt Survey

The Gould Belt is a ring of nearby star-formation regions spread across the sky.  Their proximity offers a unique opportunity to study the formation of stars in unprecedented detail.  This survey will image the densest portions of the Gould Belt with SPIRE and PACS.  It should detect hundreds of protostars and thousands prestellar condensations in the entire 145 deg2 survey - around 10 times more cold objects than already identified from the ground.  The temperature and density structures of the nearest cores will be resolved, revealing the initial conditions for individual protostellar collapse. Combined with the high resolution of Herschel, the survey will probe the link between diffuse cirrus-like structures and compact self-gravitating cores. The main scientific goal is to elucidate the physical mechanisms for the formation of prestellar cores out of the diffuse medium, crucial for understanding the origin of stellar masses.

Click here to go to the Gould Belt Survey website.

Lead Scientist: Philippe Andre (SAp/CEA Saclay)
UK contact: Derek Ward-Thompson (Cardiff University)

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The warm and dense Interstellar Medium

Far-infrared spectroscopy of the warm and dense interstellar medium using Herschel will improve our understanding of the physical and chemical processes controlling the interaction between stars and their environment.  The material is heated both by radiation from the stars and by collisions between clouds of gas and dust.  The resulting shockwaves regulate the formation of stars, and may even play a part in the way galaxies are formed.  Spectroscopy of these regions provides a natural tracer of star formation throught the Universe.  By observing a proper selection of sources, this project will give insight into the details of the physical and chemical processes controlling the interstellar medium, and thus allow astronomers to model the far-infrared emission of star forming regions.

Click here to go to the project website.

Lead Scientist: Volker Ossenkopf (KOSMA, Universitaet zu Koeln)

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Guaranteed Time (Round 1)


Probing CH and CH+ in the diffuse interstellar medium using concerted SPIRE/HIFI observations

This project will execute follow-up observations of two sources in our Galaxy already identified by Herschel's SPIRE spectrometer, regions known to contain ionised hydrogen.  Absorption by the methylidyne molecule (CH), and its cation (CH+), has been detected due to its presence in the diffuse interstellar medium between the Earth and these sources.  These detections are important to shed light on the formation processes and on the occurence of CH+, which are still outstanding questions in astrophysics.  For a better understanding of CH+ associated diffuse interstellar medium chemistry and to effectively be able to idendify the different components along the line of sight, follow-up observations with HIFI are mandatory.  We need the HIFI capabilities to separate the emission from CH+ from its absorption, to derive the kinematics of the absorptions, to assign them to individual interstellar components, and to extract relevant column densities by properly taking into account saturation effects.

Lead Scientists: Alain Abergel (Institut d'Astrophysique Spatiale (IAS)), Emmanuel Dartois (Institut d'Astrophysique Spatiale (IAS))

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Completing the OH ladder for HH46

The results from PACS observations towards the low-mass protostar HH 46 show surprisingly bright emission lines form the hydroxyl radical (OH). This radical OH plays important roles in the water and oxygen chemistry of star-forming regions and their cooling. Furthermore, the ratios of emission from water and hydroxyl are interesting tracers for ionizing radiation.  Observations of OH emission lines at wavelengths between 50 and 135 microns allows a reliable determination of the OH abundance and thus constrains water formation in protostellar envelopes.

Lead Scientist: Arnold Benz (ETHZ Institut für Astronomie)

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SPIRE-FTS observations of Young Stellar Objects revealed by SPIRE and PACS images in star formation regions

The SPIRE spectrometer will be used to obtain the spectra of a 14 young stellar objects (YSOs) that have been observed with PACS and SPIRE in imaging. These YSOs are highly embedded sources that have not been observed before at wavelengths shorter than 100 micron. The spectra will allow astronomers to ascertain their physical properties (mass and age) using chemical tracers such as the ones that trace outflows and shocks from the stars. These YSOs span a large range of luminosity, evolutionary stage and mass. The obtained spectra will constitute the first existing far-IR spectral database of YSOs.

Lead Scientist: Annie Zavagno (Laboratoire d'Astrophysique de Marseille)

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Heating and cooling mechanisms in massive star formation

The massive stars are important constituents of the interstellar medium (ISM) in our Galaxy and beyond. The processed involved in their formation and evolution influence the dynamics, energetics and chemistry of the surrounding interstellar medium both locally and on large scales. An important question to be answered is the one of cooling and heating mechanisms in regions of massive star formation. In the vicinity of massive stars, heating is provided mostly by cosmic rays and far-UV(FUV) radiation from the star itself.Cooling is mostly provided by emission of light of a variety of atoms and molecules, such as carbon, oxygen, carbon monoxide, hydroxyl and water.  This early phase when the forming massive star is still deeply embedded in its natal envelope, yet already interacting with, and potentially destroying, its environment is an important phase in the star formation process. To understand the heating and cooling balance in this phase, one has to consider the contributions of various processes such bright ultraviolet radiation from the star itself, shocks created by strong stellar winds, and the interaction between the light and the molecules. The tracers of these processes can be observed in the far-infrared, which is now accessible at unprecedented high spectral and spatial resolution with the Herschel Space Observatory. This project will observe these tracers of cooling and heating in one particular massive star forming region, called "IRAS 12326-6245", to
obtain a complete picture of the different processes, the regions they originate from and how they interact.

Lead Scientist: Carolin Dedes (ETHZ Institut für Astronomie)

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SPECHIS: SPIRE Spectral Line Surveys of HIFI-GT-KP Sources

This project will obtain several SPIRE submm line surveys of the most significant star forming regions at the highest spectral resolution allowed by the SPIRE Fourier Transform Spectrometer (FTS).  A list of 27 sources currently being observed by us with HIFI and PACS in five different Guaranteed Programs is proposed. As a result of these complementary data, the most relevant sources in the galactic center and galaxy disc (e.g. Orion) would be observed with all 3 spectrometers on board Herschel, and analyzed and interpreted by the same teams. A unique spectral data set of these sources will thus be available for the general community with a great lasting value.

Lead Scientist: Edward Polehampton (Rutherford Appleton Laboratory)

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Anatomy of Class 0 Protostellar Envelopes in their far-IR spectrum

This project will obtain spectra with the PACS Intergral Field- and SPIRE FTS Spectrometers of luminous and nearby low-mass protostellar envelopes previously categorized as Class 0 sources, which are those in the earliest stages of star formation. Our sample includes well studied sources which can be considered as templates of this early evolutionary stage of protostars. This selection of individual protostars consists the largest Herschel sample for which spectra will be taken in entire wavelength range. PACS detections of water, hydroxyl (OH) and oxygen lines will be used to determine the fundamental properties of the protostellar system, such as density, temperature, infall rate, chemical abundances and the rate at which the star is growing. SPIRE data is expected to reveal emission lines from water and help to derive the gas temperature and density using emission from carbon monoxide (CO). This will provide a valuable spectral reference database for better understanding and testing the theory of the earliest phases of star formation, allowing astronomers to examine the role of interaction between protostars ocurring in dense groups and multiple systems.

Lead Scientist: Roland Vavrek (ESAC)

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Tracing the evolution of interstellar medium from molecular clouds to stars

The aim of this project is to detect and understand how the interstellar medium (ISM) changes due to star formation. This requires a (large scale) spectral survey using the SPIRE spectrometer. The main idea is to scan with the SPIRE FTS along gradients of increasing temperature, density and star formation activity, e.g. from the edge of a star forming region, where activity is low, to its centre, where stars have already formed. Making sure to include regions of different  levels of star formation activity and clump/core density, this should probe the ISM in its different phases and see what are the relevant changes in its physical properties. Starting from the assumption that all stars in a star formation region are formed from the same material but not at the same time, this will allow astronomers to directly relate the changes in the ISM to star formation activity.

Lead Scientist: Michele Pestalozzi

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Guaranteed Time (Round 2)


High J Lines of CO as Tracers of Low Velocity Turbulent Shocks in Molecular Clouds

Molecular clouds contain supersonic turbulence. Simulations of supersonic turbulence, which include magnetic fields, show that the turbulent energy decays rapidly via shocks. Although these simulations do not explicitly follow how the energy escapes a molecular cloud, shock heated gas will cool through line radiation, thereby altering the resulting molecular spectrum of the cloud. Thus, observations of the dominant molecular coolants provide observable tracers of the turbulent energy dissipation.

We have computed models of low velocity, MHD shocks to determine which molecular species and transitions dominate the cooling and radiative energy release associated with shock cooling. By combining these models with an estimate for the turbulent energy dissipation rate from molecular clouds, we predict the strengths of these shock tracers. We find that the majority of the turbulent energy dissipated is emitted via CO rotational transitions. However, the observed low J transitions from CO in these clouds are dominated by emission from the surface layer PDR and the ambient, cool CO located throughout the cloud. The shock signature is only separable at the higher rotational transitions, J = 5-4 and up, where the emission from shock heated gas becomes dominant. The shock emission at these higher transitions is relatively weak, as these transitions are already past the emission peak of the CO ladder. Thus, to detect this unique turbulent energy dissipation signature, we require Herschel's exceptional sensitivity.

We propose to use HIFI to observe the CO J = 5-4 and 6-5 transitions towards a nearby low mass star forming region, Perseus B1-E, to verify whether shocked gas is actually present in the region. By observing multiple lines, we can determine both the temperature of the shocked gas and the characteristic shock strength. We will therefore be able to observationally constrain the turbulent energy dissipation rate in Perseus B1-E and compare this value against the predictions of supersonic turbulence decay.

Lead Scientist: Andy Pon

Allocated time: 1.3 hours

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Probing the physical conditions of pre-stellar cores on the verge of collapse

Low-mass molecular cloud cores are the birthplace of solar-type stars. Therefore, a thorough understanding of star formation requires detailed knowledge of core properties. Submm/mm observations have identified a class of very cold "pre-stellar" cores on the brink of collapse. Isolated cores, which have a relatively simple structure, are ideal laboratories for studying the star formation process; they can be directly compared with simple theoretical predictions, such as MHD simulations of single cores. Although the chemical and dynamical state of these cores has been well characterized by molecular line observations, we still lack a comprehensive understanding of two fundamental physical parameters: temperature and density. The temperature and density structure regulate the dynamical state of the objects, including any possibility for subsequent fragmentation. For the globule CB 244 we demonstrated that Herschel has the unique capability to provide this information. Due to their short free fall times (of order 10^5 years), pre-stellar cores are rare objects; therefore, we carefully target two representative well-studied pre-stellar cores. Molecular line profiles for these objects show clear signatures of infall motions indicating that they are birthplaces of new stars. The low dust temperatures of these sources (5-15 K) imply that the bulk of the emission will emerge at FIR wavelengths. We therefore propose to observe the targeted objects with PACS and SPIRE. Together with near-infrared extinction maps and submillimetre continuum data, we will be able to reconstruct the dust temperature and density maps, breaking the degeneracy with dust opacity properties. In order to disentangle the effects of dust temperature, density, and opacity, fluxes from both sides of the SED peak are required: Herschel is the only mission which can provide these data with the required sensitivity.

Lead Scientist: Amelia Stutz

Allocated time: 8.1 hours

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The Carbon Budget and Formation Signatures of Molecular Clouds

The interstellar medium (ISM) is mainly comprised of ionized, neutral atomic and molecular gas. One of the most important constituents of these phases is carbon in its ionized/neutral/molecular form (C+, C0 and CO). However, a coherent analysis of the different phases at adequate spatial resolution (Jeans length ~0.2pc) is lacking. We therefore want to re-evaluate the ISM carbon budget via observing primarily C+ at 1.9THz, C0 (at 492GHz), and CO(2-1) with Herschel, APEX and the IRAM 30m at high spatial resolution (11''-13'') for several infrared dark clouds (IRDCs). This proposal is a guaranteed time pilot study for the line of ionized carbon [CII] toward one IRDC that hosts several embedded protostars. We will follow that up in the future with an open time Herschel proposal as well as SOFIA observations. With the combined data of the different carbon phases we can address: (a) How do the relative abundances change with evolutionary stage? (b) Are the different phases mainly excited by internal or external radiation sources? (c) How important are the phase changes for the carbon cooling budget of the ISM? (d) Can we identify cloud formation signatures (e.g., turbulent flows)?

Lead Scientist: Henrik Beuther

Allocated time: 4.7 hours

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Herschel spectroscopy for very young star-forming cores: excitation, outflows, and dust emissivity

The properties of very young star-forming cores are difficult to trace. Many of their physical parameters still need to be refined observationally, before a meaningful modelling can advance. The Herschel satellite provides access to the wavelength regime where the bulk of emission arises for such objects. We plan to employ the two versatile spectrographs SPIRE-FTS and PACS-Spec in order to scrutinise eleven very young protostars comprising a larger range of masses and luminosities. The selected objects have been revealed as promisinging targets within the EPoS project. Our goals are three-fold: (1) We want to recover emission from molecular species like CO and HCO+ with SPIRE-FTS, which in combination with ground-based data enables an excitation analysis and constraints for line transfer and structure modelling. (2) We want to reveal the slope of the sub-mm continuum emission with FTS low-res spectra, which gives us a handle on the related dust emissivities. This is crucial to lift the degeneracy between column density, temperature, and dust emissivity, which usually renders an interpretation of sub-mm continuum maps ambiguous. (3) With the PACS spectroscopy for a sub-sample of two objects we want to trace the most important cooling lines of oxygen, carbon, and water to assess the thermal budget for these object stages. Of special importance is the measurement of the [OI] 63.2 micron line strength. This line gives a more direct access to the true outflow rate than common CO observations and is thus an important tool to characterise our targets which all are known to drive outflows.

Lead Scientist: Hendrik Linz

Allocated time: 8.0 hours

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The evolution of Herbig Ae/Be systems: constraining the gas and dust chemistry with herschel spectroscopy.

We propose to PACS and SPIRE spectrographic observations. The observational aim of this proposal is to characterize the emission line spectrum and continuum SED two HAe stars (HD179218 and HD50138) with the SPIRE spectrograph, and to obtain deep, high spectral sampling PACS spectra on 4 selected H2O and CH+ lines.

Lead Scientist: Jeroen Bouwman

Allocated time: 3.9 hours

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Unveiling the embedded protostellar population of the Norma cloud

Dark clouds are condensations of the ISM that are detected as silhouettes against a bright background and are known to be the cradles of forming stars. With this proposal, we aim at observing the low-mass filamentary dark cloud Sandqvist 187/188, also known as the Norma cloud. It hosts a number of low-mass protostellar objects, among which is a FU Ori star (V346 Nor). 1.2 mm continuum observations resulted in detecting 6 embedded sources that appear to be protostellar objects at different evolutionary stages. However additional data, especially at far-IR wavelengths, that are crucial to derive basic physical properties like temperature, luminosity, density and mass were insufficient so far, both in sensitivity and spatial resolution, to construct meaningful source SEDs. In addition, the global properties of the Norma cloud are also not well known. Current estimates of its density and mass are mainly based on millimetre continuum observations assuming a typical and uniform temperature. Therefore, we want to observe the star forming sites in this cloud with PACS and SPIRE imaging. The unique combination of sensitivity and spatial resolution at far-IR wavelengths provided by the Herschel Space Observatory and its instruments will be the key for determining the still badly constrained properties we are eager to obtain. With the proposed observations we want to i) fill the gaps in the SEDs of the embedded objects, ii) constrain their basic properties, iii) derive their evolutionary stage, and iv) construct a census of the star formation activity in the Norma cloud. In addition, we want to investigate the properties of the ISM surrounding these objects. In particular, we are interested in the temperature and density profiles of the dust around the embedded sources that we reconstruct from the sensitive mapping with PACS and SPIRE and subsequent SED modelling.

Lead Scientist: Markus Nielbock

Allocated time: 2.8 hours

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Tracing the evolution of the interstellar medium from molecular clouds to stars

The aim of this proposal is to study how the interstellar medium (ISM) changes due to the process of star formation. To do this we intend to perform a spectral survey with PACS and HIFI, scanning along gradients of increasing temperature, density and star formation activity e.g. from the edge of a star forming region to its centre, making sure to include regions of different levels of star formation activity and different clump/core density.

In this way we will be able to directly relate the changes in the ISM to star formation activity. This proposal is complementary to a similar ongoing proposal on the same regions with the SPIRE FTS.

Lead Scientist: Michele Pestalozzi

Allocated time: 39.9 hours

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Completion of the Gould Belt and HOBYS surveys

As demonstrated by the Herschel first highlights, both the Gould Belt and the HOBYS survey have been extremely successful. While the quality of the corresponding Herschel data is generally excellent, we have identified a few coverage or saturation problems which we intend to fix using the additional observations proposed in the present application. These observations will increase the completeness and legacy value of both surveys. We also propose a small extension to the Gould Belt parallel-mode survey of the Taurus complex in order to cover an area which shows faint 'striations' in CO observations. Combined with the existing Taurus data, the proposed extension will allow us to study, within the same cloud, the properties of the whole spectrum of filamentary structures from faint, non-star forming striations to dense star-forming filaments. Likewise, we propose to slightly extend our parallel-mode survey of the Cygnus X region, the most massive and most active star-forming complex targeted by the HOBYS key project, in order to improve the completeness of our census of high-mass protostars/prestellar cores in this important target cloud.

Lead Scientist: Philippe André

Allocated time: 16.4 hours

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A complete water map of the rho Ophiuchi cloud core A

Within only a few arcminutes, the nearby rho Oph A cloud core harbours distinctly different physical regions, i.e. gravitationally unstable dense cores, a highly collimated bipolar outflow from a class 0 protostar and photon dominated regions (PDRs) in the cloud surface layers. These regions are also spatially well separated and offer the opportunity to study in great detail the different chemistries at work, i.e. grain surface reactions, shock chemistry and UV-controlled photochemistry, all on the relevant physical scales (< 0.1 light years). The different chemistries, in turn, give rise to variations in elemental and molecular abundances, which control the energy balance of the source regions and provide feedback onto the chemistry. Although particular in some respects (detecatable amounts of O2 and H2O2), rho Oph A offers the opportunity to obtain vital general information regarding the physics and chemistry of star forming regions. We propose the extensions of our water map to include all source regions, most of which were previously not covered, as the currently available map is limited to the outflow. Simultaneously with the two ground state lines of ortho-water at 557 GHz and 1669 GHz, we also obtain the spatial distribution of the ground state line of ammonia and of a higher excitation H2O line, respectively, with HIFI. In addition, to address the still enigmatic oxygen chemistry, we propose a limited map with PACS of the elemental oxygen fine structure lines at 63 and 145 micron.

Lead Scientist: René Liseau

Allocated time: 10.7 hours

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A detailed study of the IRAS23385+6053 star forming region

We propose to use the three instruments on board Herschel to carry out a comprehensice study of the star forming region IRAS23385+6053. The region is a well-known template to host an intermediate-high mass young stellar object possibly on the verge of reaching the ZAMS. This massive YSO, detected as a strong peak in the millimeter but unrevealed below 20um, is surrounded by a population of lower mass objects of both intermediate and low mass in different evolutionary stages, and offer ideal conditions to map the star formation history in a typical region. We will determine accurate Spectral Energy Distributions and luminosities for all the compact objects, and will also ascertain if the region is at the crossroads of intense filamentary structure. Spectral maps with PACS will be obtained in [OI] and [CII], and together with other tracers from the SPIRE FTS spectral range we will be in the ideal conditions to obtain a fairly comprehensive and definitive view of the FUV irradiation conditions in the region. This will provide definitive conclusions regarding the evolutionary stage of the different YOSs in the region, enabling to draw a plausible star formation history.

Lead Scientist: Sergio Molinari

Allocated time: 4.6 hours

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Carbon isotopes in PDRs

We propose to perform deep integrations for a significant detection of the 13CII and 13CI hyperfine transitions towards five photon dominated regions (PDRs) where previous observations showed marginal, inconsistent or particularly puzzling results. These included anomalous hyperfine ratios and strong variations of the fractionation within one source. The observations will measure the absolute C+ fractionation, they will allow to distinguish the effects of isotope-selective photodissociation and chemical fractionation, and constrain the total isotopic ratio of 13C to 12C.

Lead Scientist: Volker Ossenkopf

Allocated time: 10.5 hours

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Multiepoch observations of IC 348: Using Far-Infrared Variability to Constrain the Dust Structure in Young Stellar Objects

There is growing evidence that the star formation process is in fact highly dynamic, on timescales from days to centuries. The temporal variability is a new and powerful diagnostic tool to study Young Stellar Objects (YSOs). Depending on the time-scale of the variability in the mid- and far-infrared we can learn about different physical mechanisms shaping their structure and dynamics. Here we propose to extend our near- and mid-infrared study of variable YSOs in the young open cluster IC 348 to the far-infrared (70 and 160 micron) using Herschel/PACS. We will constrain the frequency of far-infrared variability and compare the observed time-dependent behavior with protostellar and disk models to understand its origin. Possible mechanisms include fluctuations in the accretion luminosity, or echoes of inner disk structural changes projected onto the infalling envelope or flared outer disk surface. Our sample in IC348 covers a large part of the evolutionary sequence of YSOs from class I sources to transitional disks. The cadence of the requested observations allow us to study variations on time scales from days to months that could be extended to several years using our Spitzer/MIPS data.

Lead Scientist: Zoltan Balog

Allocated time: 4.4 hours

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Open Time (Key Programmes)


HIGGS: The Herschel Inner Galaxy Gas Survey

HIGGS will investigate the inflow of matter in the bulge of the Milky Way using the HIFI and PACS spctrometers on Herschel to observe emission lines from carbon, oxygen, nitrogen and carbon monoxide.  This will help determine the relationship between black holes in the centre of galaxies and the host galactic bulges, and thus the causes and mechanisms of periods of rapid star formation known as "starbursts". Studies of the gas in the bar of the Milky Way provides a means to study in detail the processes leading to starbursts. By measuring this emission and characterising the star formation that occurs under these unusual conditions, we can estimate the the mass inflow from the decaying orbits of stars. Regions lying between 600 and 6000 lightyears of the Galactic Centre that are emitting significant radiation have been identified, and HIGGS can therefore accomplish a comprehensive characterization of gas in the inner galaxy using Herschel.

Lead Scientist: Christopher Martin (Oberlin College)

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Galactic Cold Cores

This project will study starless cores and the initial conditions of star formation using Herschel and the combined power of its PACS and SPIRE instruments. As the starting point, Planck will provide the first all-sky survey of cold and compact dust clouds in the galaxy. Herschel will then concentrate on cores at mid to high Galactic latitudes, complementing other Herschel projects which observe the most prominent regions in the Galactic Plane. The main objective is to build a coherent observational database representing the entire cold core population in the Galaxy.

Lead Scientist: Mika Juvela (University of Helsinki)
UK contact: Derek Ward-Thompson (University of Cardiff)

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Herschel Oxygen Project

Oxygen is the third most abundant element in the Universe and as such it plays a decisive role in the chemistry and physics of molecular clouds. Chemical models have long predicted that some of the simplest molecules, such as carbon monoxide and water, would be the primary reservoirs of oxygen in space, and would influence the evolution of the cloud and the process of star formation. Molecular oxygen (O2) has remained elusive, the favored explanation being that oxygen atoms are tied up as water ice on grain surfaces in the cold, outer regions of clouds. This project is using HIFI to carry out a survey of regions in which the O2 abundance is predicted to be large. The selected sources include regions of heated gas surrounding embedded young stars, regions with intense radiation, and regions which contain shockwaves from collisions of clouds of gas and dust. We expect that these sources will be of small angular size, and can be observed using beam switching in mini line survey mode, to enable sideband deconvolution and minimize interference from confusing lines of other species. The greatly improved sensitivity of HIFI receivers and the far smaller Herschel beam relative to previous missions allows the verification of important aspects of models of these regions, probing critical chemistry and physics in regions that are tracers of recent and prospective star formation.

Lead Scientist: Paul Goldsmith (Jet Propulsion Laboratory)

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Hi-GAL: the Herschel infrared Galactic Plane Survey

Dust is one of the most important tracers of the structure and physical conditions of the interstellar medium throughout the lifecycle of a galaxy. From diffuse interstellar cirrus, to dense molecular clouds, and from protostars to supernova remnants, the equatorial plane of our Galaxy provides the ideal laboratory to carry out investigations of the properties of the different constituents of the interstellar medium.  Hi-GAL uses PACS and SPIRE in parallel mode, which is explicitly designed to allow observations of large areas of the sky with both cameras simultaneously. The inner third of the Galactic Plane will be covered by 55 2ox2o tiles, allowing a number of key science questions to be answered.  These include: the distribution and temperature of dust throughout the Galaxy; the complete evolutionary sequence of stellar birth from interstellar clouds to stars; the nature of thresholds for the formation of stars; use what we learn from our Milky Way to understand distant galaxies.  Hi-GAL is allowing significant advances in all these issues, and will become a cornerstone to unveiling the formation of stars and the evolution of galaxies.

Click here to go to the Hi-GAL website.

Lead Scientist: Sergio Molinari (INAF - IFSI)
UK contact: Toby Moore (Liverpool John Moores University)

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HOPS: the Herschel Orion Protostar Survey

Understanding protostellar evolution is a necessary step toward characterising the factors which ultimately determine the properties of emerging stars and their planetary systems. HOPS is using PACS for imaging and spectroscopy of protostars identified in Spitzer surveys of the Orion molecular cloud complex. This is the richest known sample of protostars at a common distance within 1500 light years of the Sun. Images are being obtained for 283 protostars ranging in brightnesses from 1/10th to a thousand times the brightness of the Sun, and spanning a range of ages. In concert with existing infrared images and spectra, the PACS images will be used to determine the fundamental properties of the protostellar envelopes and disks. As well as the imaging, spectroscopy of 37 protostars will be used to measure emission water vapor, hydroxyl and oxygen from the pre-stellar envelopes, in the accretion shock onto the central protostellar disk, and in outflows. These data are providing an unparalleled view of the flow of material from the pre-stellar envelope onto the disk, through the disk to the star, and away from the star in outflows. The Orion molecular cloud complex contains an exceptionally wide range of physical conditions, and by comparing the properties of protostars in different regions of the Orion clouds it is possible to assess the roles of these conditions on protostellar evolution. These observations are producing a unique legacy dataset for guiding and testing a theory of protostellar evolution.

Click here to go to the HOPS website.

Lead Scientist: Tom Megeath (University of Toledo)

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GOT C+: Galactic Observations of the Terahertz C+ Line

Star formation activity throughout the Galactic disk depends on the physical state of the interstellar gas, which in turn depends on it temperature and the surrounding environmend. To understand these processes we need information about the properties of the gas clouds and regions of intense radiation. An important tracer of these regions is emission by ionised carbon (C+) at 158 microns. The GOT C+ project is using HIFI to observe over 900 locations throughout the Galaxy, providing the astronomical community with a large database of the diffuse cloud properties.  This will increase the understanding of the interstellar medium in the Milky Way and, by extension, in other galaxies. Ionised carbon is present throughout the Galactic plane, and is the strongest far-infrared emission line in the Galaxy. Combined with other data, it can be used to determine density, pressure, and radiation environment in gas clouds.  Herschel is the best opportunity over the next several years to probe the ISM in this tracer and will provide a template for large-scale surveys with dedicated small telescopes and future surveys of other important ISM tracers.

Lead Scientist: William Langer (Jet Propulsion Laboratory)

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Open Time (Round 1)


Warm HCN in the planet-formation zone (R<50 AU) of GV Tau

Spitzer NIR observations revealed the presence of warm C2H2 and HCN with large gas phase abundances in the disk around GV Tau N. The emission of these molecules has been interpreted as originated in the disk at R<50 AU, i.e., in the planet formation zone. Recent observations by our team of the HCN 1-0 and 3-2 lines using the IRAM 30m telescope and the Plateau de Bure Interferometer give further support to this interpretation. We propose to complete the mm and NIR observations by observing the HCN 7-6, 11-6 and 13-12 lines with the instrument HIFI on board Herschel. These detections will allow us to carry out a complete study of the HCN excitation, and to estimate the physical conditions (gas temperature and density), the radius and the kinematics of the emitting region. In addition, we will observe key CO and H2O lines in order to determine the amount of warm gas and derive the HCN and H2O abundance in the inner region of this young disk. To determine the physical conditions and chemical composition of this inner disk gas is the key to understand the evolution of the volatile material that becomes incorporated into the planet-forming regions.

Lead Scientist: Asuncion Fuente

Allocated time: 4.6 hours

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Physical conditions in PDRs

Luminous stars have a profound influence on their environment as their far-UV (6-13.6 eV) photons dissociate and ionize surrounding gas. The gas in these so-called PhotoDissociation Regions (PDRs) is heated by the photo-electric effect on polycyclic aromatic hydrocarbon (PAH) molecules and very small grains (VSG) and cools through emission in atomic fine-structure ([OI], [CII], [SiII]) and molecular rotational (H2, CO) lines. PDR models are known to have intrinsic problems and have moreover only been tested using observations with very large beams on complex regions. Herschel’s high sensitivity, high spatial resolution, and wide wavelength coverage allows for the first time a study of the far-IR spectra of spatially resolved PDRs. We propose to map the key diagnostic, far-IR and sub-mm, atomic ([CII] 158μm, [OI] 63, 145μm) and molecular (CO) lines using PACS and SPIRE in a sample of edge-on, spatially resolved Galactic PDRs. The sources in this sample are all well-studied over a wide-wavelength range and have all been mapped by IRS/Spitzer in the rotational H2 lines, the [SiII] 34μm line, the PAH features and the VSG continuum. The goals of our combined Herschel/Spitzer study are to determine the density and temperature structure of the region, to quantify the gas energetics (cooling/heating efficiency), and to compare the gas (heating) characteristics with the emission characteristics of the (neutral & cationic) PAHs and VSGs. This will provide deep insight in the photo-electric heating of atomic gas which is central to the structure of PDRs, the phases of the ISM, and the structure of protoplanetary disks. In addition, these well-known Galactic PDRs provide natural laboratories for studies of the interaction of massive stars with their environment and a semi-empirical way of calibrating the infrared characteristics of regions of massive star formation and, thus, the observational characteristics of galaxies out to the early Universe.

Lead Scientist: Alexander Tielens

Allocated time: 21.1 hours

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Probing the physics and dynamics of the hidden warm gas in the youngest protostellar outflows

We propose to obtain PACS and HIFI spectroscopic maps of five outflows driven by young and heavily embedded ‘‘Class 0’’ protostars, in selected transitions of [OI], CO and H2O. These species represent the main coolants of the warm (T ~ 100-2000 K) and dense (10^4 cm^{-3}-10^6 cm^{-3}) shocked gas that gives rise to most of the radiative luminosity of these systems. The immediate objectives of the proposed observations will be: 1) to detect, through a map of the [OI]63um line, the embedded atomic primary jet that should be responsible for the acceleration of the outflow; 2) to map the excitation structure of the molecular warm gas component and understand its role in the dynamics of the system; 3)to derive the spatial variations, as a function of the central source, of the H2O abundance and O/H2O abundance ratio, that will be tracing time-dependent chemical changes during the flow life-time. In order to maximize the scientific return from this program, we have selected sources that will be already mapped in the H2O 557 GHz line within the WISH Key Program. If added to the ground-based and space-borne spectral maps already available for the selected objects, the proposed Herschel observations will represent the first multi-wavelength spatial study of protostellar outflows covering the complete spectral domain of emission (from NIR to mm) of these objects. Such a data-base has a strong legacy value for both future missions and development of theoretical models and numerical simulations of shocks and outflows.

Lead Scientist: Brunella Nisini

Allocated time: 53.7 hours

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Peering into the protostellar shocks: NH3 emission at high-velocities

Ammonia and water are key molecules for determining the physical and chemical structure of star forming regions because of their large abundance variations. In shocked regions where jets driven by low-mass protostars impact the surrounding medium, the NH3 and H2O abundances undergo a dramatic enhancement due to ice grain mantle sublimation. Thanks to the very recent HIFI (CHESS KPs) observations performed towards the prototype L1157 outflow, we compared the line profiles due to the NH3(1_0-0_0) and H2O(1_10-1_01) transitions in the HIFI-band 1b. The high-spectral resolution provided by HIFI allowed us to observe a striking difference in profile between water and ammonia, with H2O emitting at definitely higher velocities. In Codella et al. (2010) we propose that such difference reflects different formation mechanisms: while NH3 is believed to be a direct product of grain surface reactions, water is enhanced by the release of the icy mantles as well as by endothermic reactions occurring in the warm (> 220 K) shocked gas, which convert all gaseous atomic oxygen into water.

We propose here the obvious next step, i.e. to observe the NH3(1_0-0_0) line at 572.5 GHz in a sample of 8 bright low-mass outflow spots already observed in the H2O(1_10-1_01) line within the WISH KP. The analysis of the profiles in such sample will allow us to: (i) determine whether the difference in profiles is unique to L1157 or a common characteristic of chemically rich outflows; (ii) provide clues to the physical characteristics of the shock and of the pre-existing material. Such analysis will be performed by using a suite of chemical, PDR, radiative transfer and shocks models which our team has developed.

The present proposal can be considered as a WISH+CHESS KPs synergy and indeed it gathers components of the teams leading the investigations of protostellar outflows in both CHESS and WISH Herschel GT-KPs.

Lead Scientist: Claudio Codella

Allocated time: 15.8 hours

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Physics of gas evaporation at PDR edges

Far-ultraviolet (FUV) photons in massive OB star-forming regions have a major impact on the structure, dynamics, chemistry and thermal balance of their associated molecular cloud. We propose to study the photoevaporation under FUV irradiation of dense filaments in prototype photodissociation regions (PDR) by mapping with the HIFI spectrometer the [CII] 158 micron line associated with the evaporating gas and high-J CO lines tracing the warm dense structures. The combination of the spectral range covered by Herschel and the very high spectral resolution of HIFI is unique to get insight into the process of mixing of cold molecular gas into warm atomic gas. This process governs the evolution of dense gas submitted to FUV photons in a wide variety of astronomical objects including protostellar and protoplanetary disks but is best studied in PDRs. We ask for 9.8 hours of observations in two PDRs, NGC7023 and the Horsehead nebula. NGC7023 is illuminated by a B2Ve star and hosts very diluted atomic gas and dense filaments. The Horsehead nebula is a PDR viewed nearly edge-on with a high gas density gradient at the edge that is illuminated by a O9.5V star and is immersed in an HII region. In these objects, there is evidence for dynamical processes that create a mixing layer between molecular and atomic gas, both from gas kinematics (first results with HIFI on the [CII] line) and chemistry. The first HIFI [CII] results clearly call for a larger spatial coverage of the region using OTF mapping mode with HIFI to obtain a more complete picture of the PDR morphology and dynamics. The 12^CO(8-7) and 13^CO(8-7) lines will be also targeted to trace the warm interfaces of the dense filaments/edges. The team gathers together specialists of the studied regions and of the Herschel instruments: HIFI (this proposal), SPIRE and PACS (complementary data). The team has strong expertise in the study of the physics and chemistry of PDRs, both in terms of data analysis and modelling using and developing the Meudon PDR code.

Lead Scientist: Christine Joblin

Allocated time: 9.8 hours

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Investigation of the nitrogen chemistry in diffuse and dense interstellar gas

We propose to investigate the interstellar chemistry and physics of nitrogen through Herschel/HIFI observations of simple nitrogen-hydride molecules including NH, NH2, NH3, and related ions. The nitrogen chemistry is still rather uncertain and we therefore propose to compare and contrast the abundances and ortho/para ratios of nitrogen hydrides in the diffuse interstellar gas to the dense cores of molecular clouds. This comparison can be done very efficiently by observing excited-state transitions in selected cores that have previously been used in the PRISMAS program as background sources for absorption measurements in the ground-state transitions. In this way, we will determine whether nitrogen chemistry is dominated by gas-phase reactions or by processes on surfaces of dust grains, and whether the dominant chemistry is different in different parts of the interstellar medium. In summary, we propose HIFI observations of 5 transitions of simple nitrogen-bearing molecules in 8 sources, and 3 transitions in 2 sources. The total requested observing time is 26.2 hours.

Lead Scientist: Carina Persson

Allocated time: 18 hours

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Deuterated water chemistry towards high-mass star-forming regions.

Observations of the HDO molecules are an important complement for studies of water, since they give strong constraints on the formation processes: grain surfaces versus gas-phase chemistry through energetic process as shocks. HIFI observations of multiple transitions of HDO in SgrB2(M) combined with ground-based observations allowed for the first time the determination of its abundance throughout the envelope. In the framework of the PRISMAS Key Program, a large sample of high-mass star-forming regions have been observed with the detection of many species in their line of sight. The HDO (111-000) fundamental transition has also been detected in absorption at the velocity of the hot core towards the 2 sources that have been observed so far, probably tracing the colder envelope in its surrounding.

We propose to observe higher energy level HDO transitions towards a sample of three compact HII regions that will be targeted by the PRISMAS Key Program (G34.3+0.1, W33A, W49N) in order to perform a full modeling from the hot core through the envelope using a spherical Monte Carlo radiative transfer code, RATRAN, which takes into account radiative pumping by continuum emission from dust. We will use for an optimum accuracy of the modeling the HDO and D2O collision rates with H2, recently computed within our group, that are not available in the public so far.

This study will hopefully give strong constrains on the formation processes of water, combining the proposed observations with published or soon to be published high resolution H2O observations with HIFI towards the same sources.

Lead Scientist: Charlotte Vastel

Allocated time: 15.3 hours

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Hot Dust within HII Regions

We propose observing thermal dust emission inside two wind blown bubbles identified by their PAH emission (N90 and N56 from a Churchwell et al., 2006) in all SPIRE and PACS bands. These bands sample emission from all dust grain sizes and temperatures thought to exist behind the post shocked gas. By measuring the emission across the face of the bubble and comparing with numerical simulations, we will determine how the grain size distribution changes with distance from exciting source. These results will help determine what dominant physics, sputtering or gas-dust friction, dominates grain processing within these sources. We will also measure emission from the cold, dense cloudlets proposed by Everett & Churchwell (2010) as the source of dust within these bubbles. By better characterizing these physical properties of dust grains, we will be able to better predict how dust grains affect the energetics of wind blown bubbles.

Lead Scientist: Christer Watson

Allocated time: 5.6 hours

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The Conditions of Isolated Dark Clouds with Signs of On Going H2 Formation

We propose to map three nearby isolated dark clouds, CB 45, B227, and L1574 with SPIRE. They are carefully selected based on their intriguing morphology of displacement between CO, 2MASS extinction, atomic gas traced HI Narrow self-absorption (HINSA),which is a unique tracer of cold atomic gas INSIDE molecular clouds. SPIRE maps will provide crucial dust emission information for quantifying dust column density, dust temperature and dust properties. SPIRE will provide much higher resolution than 2MASS extinction and is capable of tracing relatively diffuse dust structure missed by 2MASS. Combining HINSA, molecular gas, extinction, and dust emission data, we will have an unprecedented comprehensive data set for understanding the transition from atomic to molecular ISM. The spacial information and high sensitivity provided by SPIRE will enable us to construct time dependent H2 formation model for realistic clouds. Such a model will provide quantitive answers, for the first time, to fundamental questions in star formation, such as "How molecular are molecular clouds?" and "What is the age of a dark cloud?".

Lead Scientist: Di Li

Allocated time: 1.3 hours

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Ammonia as a Tracer of the Earliest Stages of Star Formation

Stars form in molecular cloud cores, cold and dense regions enshrouded by dust. The initiation of this process is among the least understood steps of star formation. High−resolution heterodyne spectroscopy provides invaluable information about the physical conditions (density, temperature), kinematics (infall, outflows), and chemistry of these regions. Classical molecular tracers, such CO, CS, and many other abundant gas−phase species, have been shown to freeze out onto dust grain mantles in pre−stellar cores. However, N−bearing species, in particular ammonia, are much less affected by depletion and are observed to stay in the gas phase at densities in excess of 1e6 cm−3. The molecular freeze−out has important consequences for the chemistry of dense gas. In particular, the depletion of abundant gas−phase species with heavy atoms drives up abundances of deuterated H3+ isotopologues, which in turn results in spectacular deuteration levels of molecules that do remain in the gas phase. Consequently, lines of deuterated N−bearing species, in particular the fundamental lines of ammonia isotopologues, having very high critical densities, are optimum tracers of innermost regions of dense cores.

We propose to study the morphology, density structure and kinematics of cold and dense cloud cores, by mapping the spatial distribution of ammonia isotopologues in isolated dense pre−stellar cores using Herschel/HIFI. These observations provide optimum probes of the onset of star formation, as well as the physical processes that control gas−grain interaction, freeze−out, mantle ejection and deuteration. The sensitive, high−resolution spectra acquired within this program will be analyzed using sophisticated radiative transfer models and compared with outputs of state−of−the−art 3D MHD simulations and chemical models developed by the members of our team.

Lead Scientist: Dariusz Lis

Allocated time: 26.3 hours

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Studying diffuse interstellar clouds with observations of hydrides

With the use of the HIFI instrument, we propose to observe four simple hydride molecules - HF, OH+, H2O+, and H2Cl+ - in absorption towards five bright submillimeter continuum sources. The target sources, all located in the Galactic plane with sight-lines that intersect multiple interstellar clouds, are the massive star-forming regions W49N, W51, G29.96-0.02, W3(OH), and G330.95-0.17. This selection of sources samples sight-lines in the 1st and 4th quadrants of the Galaxy and in the outer Galaxy. The proposed observations will have integration times sufficient to obtain signal-to-noise ratios in the range 100 - 400 in a single spectral channel, providing great sensitivity to absorption by foreground material. We will thereby determine the molecular column densities in foreground clouds located in spiral arms that lie along the sight-lines to these continuum sources. The four molecules we will observe, all detected previously in the ISM in early Herschel observations, will provide critical information about the diffuse interstellar medium. In particular, HF will permit the identification and study of clouds with a very small H2 column density that may be virtually undetectable in the spectra of other molecules; OH+ and H2O+ will allow us to study clouds with a small molecular fraction (revealed by a large OH+/H2O+ ratio), and to determine the cosmic ray ionization rate as a function of Galactocentric radius; and H2Cl+ will probe the photoionization rate and its variation with position in the Galaxy.

Lead Scientist: David Neufeld

Allocated time: 34.8 hours

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An accurate mass measurement for prestellar cores

Prestellar cores are crucial to our understanding of star formation. It is at this evolutionary stage that the stellar mass is set. If we are to understand the origin of the stellar IMF, we must therefore study the masses of the prestellar cores from which the stars are formed. There is currently a large uncertainty in the measured prestellar core mass that we obtain from far-IR and submillimetre observations. This uncertainty is caused by our inability to simultaneously determine the column density, temperature and dust emissivity index from photometric observations. Physical processes such as grain growth, or ice-mantle formation, which are affected by changes in density and temperature, will change the dust emissivity index. By simply taking a canonical value for the emissivity index, we cannot determine the correct mass for prestellar cores.

The SPIRE FTS allows us to break this degeneracy for the first time, and simultaneously measure the column density, temperature and dust emissivity index, and therefore determine accurate masses. We propose to map 16 prestellar cores with the SPIRE FTS, and hence generate accurate maps of their column density. We will map each core using the full FTS field of view. We will be able to determine the absolute value of the dust emissivity index, and also see whether it varies across each of the cores. We have selected cores in different environments in order to study the core-to-core, and cloud-to-cloud variations in the dust properties. We will be able use this information about the relation between the three measured parameters, to more accurately determine masses for a much larger sample of cores for which only photometric data are available.

Lead Scientist: David Nutter

Allocated time: 11 hours

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A Systematic Survery of the Water D to H Ratio in Hot Molecular Cores

The D/H ratio of water and the enrichment of HDO relative to H2O in comets, oceans, and interstellar water vapor, has been posited as one of the primary links between chemistry in the cold (T = 10-20 K) dense interstellar medium (ISM) and chemistry in the Solar Nebula. However, there are only ~10 measurements of HDO/H2O, even in hot (T > 100 K) molecular cores, which have the most favorable chemistry (due to fossil evaporation of D-enriched ices) and excitation. In addition the existing measurements have a wide range of uncertainty, making it impossible to discern the presence of source-to-source variations, which could hint at the origin of deuterium enrichments in the dense ISM. We propose here to change this statistic with a systematic survey of HDO and H2O in a sample of 20 hot molecular cores spanning a two order of magnitude range in mass and luminosity. This will increase the number of known water D/H ratios by ~200%. This program is unique in scope for Herschel and requires the uniformity in calibration and high spectral resolution offered by the HIFI instrument. With the stability of HIFI we will be able to derive D/H ratios with significantly less uncertainty. Our observations will be combined with theoretical chemical models to explore the statistics offered by this sample. By looking at a large number of objects with a range of conditions we aim to unlock the secrets of water deuteration in the interstellar space.

Lead Scientist: Edwin Bergin

Allocated time: 18 hours

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Low gas to dust ratio in proto-planetary disks: the Carbon content of CQ Tau, MWC 758 and MWC 480

The study of the transition from gas-rich protoplanetary disk to gas-poor debris disk is crucial to constrain the planetary formation mechanisms. Although it is a key parameter for big gaseous planet formation, the evolution of the gas-to-dust ratio with time and star properties is not yet known. One of the first steps to observationally constrain it is to determine independently the gas mass and the dust mass of disks. The dust content, determined from continuum emission, is better known than the gas content. As molecular hydrogen is not observable at the low temperatures of disks, the gas mass is usually derived from CO observation. However, CO may not be always the main carbon reservoir: it should freeze on grain mantles in the cold mid-plane of T Tauri disks, and be photodissociated in the upper layers by the UV field, leading to CI and CII, especially in disks surrounding A stars. We propose here to characterize the gaseous Carbon content in three disks (CQ Tau, MWC 758 and MWC 480) using the three main C carriers: CO, CI and C+. Previous CO observations indicates warm disks (the temperature being well above the CO freeze-out temperature). Two of them, CQ Tau and MWC 758, have very low CO content and may be in the transition stage between gas-rich and gas poor disks. A low CI content was also found for CQ Tau using APEX. We propose to take advantage of sensitivity of Hershel at 1900 GHz (157 um) and high spectral resolution provided by the HIFI instrument to observe C+ in these disks.

Lead Scientist: Edwige chapillon

Allocated time: 6.4 hours

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The Herschel/HIFI insight on the CH+ puzzle

Seventy years after its discovery in the diffuse interstellar medium, the origin of the CH+ cation is still elusive. Herschel/HIFI offers a unique opportunity to disclose the underlying gas dynamics at the origin of CH+ in the diffuse medium by allowing high sensitivity and high spectral resolution observations of the CH+ (J=1-0) transition, unreachable from the ground: it will be the leading and only instrument and the observations will bring a completely new look at this resilient puzzle.

The abundant CH+ ion is not only a sensitive tracer of the most tenuous phases of the interstellar medium but it is likely a specific tracer of turbulent dissipation, because its formation route is highly endoenergic. We propose absorption spectroscopy observations of mainly the CH+ J=1-0 line, against 10 background dust continuum sources, bright enough to allow us to sample a broad variety of galactic environments. The lines-of-sight will probe the outskirts of star-forming regions, including one InfraRed Dark Cloud, where turbulent dissipation is most intense, and diffuse gas at high galactic latitude where turbulence is milder. The primarily goal of this project is the comparison of the CH+ abundances with model predictions of turbulent dissipation regions, in which dissipation proceeds either in low-velocity shocks or intense velocity-shears. Another goal is testing the possibility that CH+ forms at the turbulent interface between the two thermally stable phases of the interstellar medium.

As HF, CH+ is a potential sensitive tracer of diffuse matter in the early universe. Understanding its origin and the dissipative processes that it traces will shed a new light on galaxy formation and evolution.

Lead Scientist: Edith Falgarone

Allocated time: 38.7 hours

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Characterization of the long wavelength features of interstellar Polycyclic Aromatic Hydrocarbons

Strong emission features at 3.3, 6.2, 7.7, and 11.2 um dominate the mid-infrared spectra of most interstellar objects. These IR features are due to vibrational fluorescence of large (50-150 C-atom) Polycyclic Aromatic Hydrocarbon molecules pumped by UV photons. These species will also have bands at far-infrared wavelength, notably due to `drum-head’ modes. We have performed experimental and theoretical studies that demonstrate that these bands carry unique information, particularly on the size of the emitting species that cannot be obtained from the shorter wavelength bands.

We propose to measure the far-IR spectra of a sample of well-studied PAH sources using PACS and SPIRE. The sample has been carefully selected to show strong mid-IR PAH bands, and a relatively weak dust continuum at the Herschel wavelengths to maximize the line-to-continuum ratio for far-IR PAH bands. These observations are designed to measure infrared bands to a level of 1% of the dust continuum. Together with the Spitzer/ISO studies, the full spectrum of the IR emission features from 3 to 600 um can be determined. In order to determine the implications for the emitting PAHs, we will compare these bands to the PAH database that we have compiled over the last 15 years and analyze the emission using the realistic PAH emission model that we have developed over the years.

Lead Scientist: Els Peeters

Allocated time: 9.4 hours

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Investigating the origin of the far-infrared emission of the microquasar Cygnus X-1

Microquasars are Galactic X-ray binaries exhibiting collimated outflows commonly called jets. In particular, the so-called compact jets are detected almost simultaneously in all the spectral domains, and are characterised by the existence of a spectral break at which they change their emission regime from optically thick to optically thin synchrotron. The determination of this cut-off frequency is fundamental for the understanding of the accretion-ejection processes as it is related to the black hole spin and mass, as well as to the accretion rate. In a previous Spitzer spectroscopic study of Cygnus X-1, we assessed the contribution of the compact jets to the mid-infrared continuum as well as their spectral break. Nevertheless, its accurate value appears to be dependent on the model used to describe the continuum of the companion star, which is the blue supergiant HD226868. Indeed, it changes whether we consider bremsstrahlung from the stellar winds or thermal emission from a circumstellar dust component. We therefore require photometric observations of Cygnus X-1 with PACS, in the blue, green, and red filters, in order to assess the flux density level of the source at 70, 100, and 160 microns. These measurements, combined with our Spitzer spectra, will allow us to discriminate between bremsstrahlung and dust, which will eventually lead us to the accurate determination of the spectral break of the compact jets exhibited by Cygnus X-1.

Lead Scientist: Farid Rahoui

Allocated time: 6.2 hours

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Water Formation and Destruction Processes in Molecular Clouds

The study of water is one of the most compelling and unique science goals of the Herschel mission. Unfortunately, our understanding of water may not be limited by the quality of the data so much as by remaining uncertainties regarding the processes that govern the formation and destruction of water. We propose a set of focused observations designed to measure the depth-dependent distribution of water vapor, which is sensitive to a set of processes (e.g., photodissociation, photodesorption, grain surface reactions) that not only determines the distribution of water, but affects the abundance and distribution of many other gas-phase molecules. The knowledge gained will not only improve chemical models for which these processes are important, but will greatly improve our estimates of the true water-vapor abundance derived from all Herschel measurements. We propose a set of HIFI and PACS water maps, pointed observations, and strip scans toward three objects whose face-on or edge-on appearance makes them ideal laboratories for this study: Orion, Cepheus B, and DC 267.4-7.5. Our prior SWAS observations provide confidence in the presence of the water emission we seek to detect as well as proof that the proposed study is feasible. We also make use of ground-based molecular line maps that have already been obtained. This study is not a part of the WISH program, nor can it be carried out with WISH data. The choice of HIFI instead of SPIRE for this study is driven by the need for both sensitivity and velocity resolution - it would require > 2000 hours for SPIRE to obtain a sparsely-sampled map of the same area (23.5’x40’) and sensitivity (9.E-18 W/m2, 10-sigma) as the fully-sampled 557 GHz map we propose toward Orion alone and, with HIFI, the water lines will be velocity resolved, which is key to the success of this study. Finally, a by-product of this study will be one of the largest velocity-resolved water maps to be made by Herschel. The total time required for this Herschel-unique program is 38.5 hours.

Lead Scientist: G.J. Melnick

Allocated time: 10 hours

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A Herschel Study of Star Formation Feedback on Cloud Scales

We propose to conduct a study of the impact of radiative and mechanical stellar feedback on the surrounding medium of a cluster-forming cloud. Outflows and UV radiation from young stars affect the dynamics and the chemistry of the gaseous environment, thereby influencing the star formation process in the cloud. Herschel offers an extraordinary opportunity to observe unique tracers of these important physical and chemical processes. Our observations will mostly consist of unbiased HIFI, PACS, and SPIRE spectral maps of NGC1333, a nearby cloud, that harbors a cluster of protostars, many outflows and a couple of B stars, and it is commonly used as the prototypical cluster to model clustered star formation. These maps will allow us to conduct a study of an unbiased sample of shocks from outflows at different evolutionary stages within one cloud. We will use important shock tracers and coolants that typically cannot be observed from the ground to investigate the chemistry and physics of the outflow phenomenon in order to fully understand their impact on the natal cloud. Our study will provide the most complete estimate of the outflow energy and momentum input budget in a cluster. In addition, we will investigate how stellar UV radiation affect the water abundance, its formation and destruction, and the chemistry of the gaseous environment. Our proposed Herschel observations (and complementary ground-based data) will provide the best estimate of the water mass reservoir for star formation at the scales of the cloud. The resulting data sets for this cluster-forming region will surely provide a long term observational basis against which to test current and future models of cloud chemistry, stellar feedback and shocks.

Lead Scientist: Hector G. Arce

Allocated time: 51.5 hours

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A Study of the Small Negative Molecular Ions CN-, CCH-, and OH- in the Interstellar Gas

The HIFI instrument on Herschel provides a unique opportunity to undertake an astronomical study of light negative molecular ions in the interstellar gas, as these are difficult or impossible to observe from ground based observatories. A sensitive search for the negative ions CN-, CCH-, and OH- with HIFI toward 6 galactic molecular sources is proposed. Three successive rotational transitions (J=6, 7, 8) of CN- and CCH- in HIFI bands 1 - 3, and the lowest rotational transition of OH- near 1.12 THz will be observed. The goals of this study are: i. to enlarge the number of known sources of light negative molecular ions; ii. to determine the abundances of the anions, as well as the anion-to-neutral ratios to assess theoretical models of the fractional ionization of molecular clouds; and iii. to assess the chemical environment of anions through parallel observations of neutral molecules (H13CN and HNC) and positive molecular ions (CO+ and H13CO).

Lead Scientist: Harshal Gupta

Allocated time: 37.2 hours

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Massive Young Stars in W43: PACS/SPIRE SED Spectral Scans of MM1 to MM4

 

We propose to acquire complete spectral-scans of the four most luminous and massive young stellar objects (MYSOs) in the giant W43 giant HII region complex located at a distance of 5.5 kpc in the Galactic Molecular Ring. The SED modes of the PACS spectrometer and the high-resolution mode of the SPIRE FTS will be used to trace variations in chemical abundances, excitation conditions, and structure in the SEDs as functions of the evolutionary states of these four massive objects. While the central pixels record the spectra of the target MYSOs, the adjacent pixels will probe the spectral properties of the surrounding dense molecular clumps, additional massive YSOs that happen to fall within the aperture, PDRs, and adjacent ionized regions. W43 is one of the most luminous star forming regions in the Galaxy. It has undergone a `mini-starburst' within the last few Myr. Massive star formation continues in at least 50 clumps spread over a 20 pc diameter region. The proposed observations will test evolutionary models for MYSOs.

Lead Scientist: John Bally

Allocated time: 6.7 hours

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EPICS: Evolution of Protostellar Ices, Carbonates and Silicates

Dynamical and energetic processes that occur during the evolution of a protostar have a strong influence on composition and other characteristics of the dust and these can be well probed with far-IR spectroscopy using Herschel's PACS instrument. Physical evolution of protostars, driven by gravity, is accompanied by a dramatic evolution of the dust, driven by condensation and coagulation, thermal processing by the central star, and shocks driven by protostellar jets. Mid-IR spectroscopic studies of dust in protostellar environments reveal a wide diversity of dust components ranging from volatile ices, to carbonates to refractory crystalline silicates. However, the relationship between the dust evolution and the evolution of the protostar itself has not yet been studied. The evidence suggests that ices are connected to the deepest embedded phase, while crystalline silicates may trace the presence of disks. Carbonates may be either connected to processing of ices in the envelope of YSOs or result from disk processes. In order to probe this dust evolution that accompanies protostellar evolution, we have carefully selected a sample of well-characterized protostars spanning a wide range in evolutionary age and protostellar characteristics from the deeply embedded class 0 stage through the accretion disk (class I) and protoplanetary disk (class II) phases. We will employ PACS in SED mode to study the lattice vibration phonon modes of the ices, silicates and carbonates that occur in the 51 to 220 micron region. Our proposed study will allow us to address at what stage of protostellar evolution different dust signatures become apparent. In this way, we can address the (inter)relationship of these different compounds and the processes involved in their formation. Our study directly addresses Herschel's top-level goal of studying the ingredients in the dust throughout the evolution of a protostar that will then become part of the planetesimal and planet-forming process.

Lead Scientist: Jean Chiar

Allocated time: 31.9 hours

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A 3-Dimensional view of the ionized and the warm neutral gas in Orion

While bolometric images provide a ``snapshot'' of the impact of high-mass star formation over entire molecular cloud complexes, it is only by pursuing large scale maps of different spectrally-resolved line tracers of the ionized and the warm neutral gas that we can probe and study the cloud dynamics and kinematics in detail.

We propose to use HIFI to carry out large scale mapping of the core of the Orion GMC (7.5'x11.5'), the closest high-mass SFR in the disk of the galaxy. Our goal is to study the impact and feedback of the high-mass star formation process on the parental molecular cloud by following the ionized, the warm neutral gas and the dense molecular gas over large scales and at high spatial resolutions. The global cloud dynamics, the kinematic interplay of the different gas phase components and their influence on the environment will be revealed by a series of velocity-resolved [NII], [CII], CH+, CH, high-J CO, HCO+ and HCN line maps that cannot not be observed from the ground.

Lead Scientist: Javier R. Goicoechea

Allocated time: 27.7 hours

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FOOSH: FU Orionis Objects Surveyed with Herschel

We propose to utilize the unprecedented spatial resolution and sensitivity of Herschel at far-infrared and submm wavelengths to observe nearly all known FU Orionis objects, the dramatic result of burst accretion events in protostellar disks. The known FUors represent a vital window into a key process of star formation rather than a rare and peculiar event in the lives of a few stars. In addition, FUors provide a natural laboratory that probes the effect on enhanced heating on disk composition and structure. Our objectives are to (1) Study the structure of known envelopes and constrain the amount of remnant envelope material around the remainder; (2) characterize the physical and chemical properties of the disks and envelope, the parameters that set the initial conditions for planet formation in T Tauri disks; (3) observe solid-state, atomic, and molecular spectral features toward FUors in order to determine the effects of increased luminosity on mineralogy, disk chemistry, and envelope material. In order to do this we will use all three instruments onboard Herschel, providing a comprehensive survey of FUors.

Lead Scientist: Joel Green

Allocated time: 21 hours

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Low efficiency clouds and the minimum conditions for star formation

To understand the conditions required for star formation, the best regions to observe are regions where those criteria are only just fulfilled - molecular clouds with low star formation efficiencies (SFE). The Scorpius molecular complex contains 4000 solar masses of molecular gas, yet Spitzer observations show it contains only 11 young stellar objects hence an extreme SFE of less than 0.3%. Its low SFE can be contrasted with the rich L1688 protostellar cluster in nearby Ophiuchus and intermediate SFEs in Lupus, with which it shares a similar environment on the boundary of the Lupus-Sco-Cen OB association. We aim to map the Scorpius clouds with SPIRE and PACS to locate and characterise the dense cores, identifying gravitationally unbound, bound and protostellar cores. We aim to determine why regions such as this have such low SFE, the evolutionary path(s) for starless cores, and the minimum conditions for star formation. At 130 pc, Scorpius is among the closest star forming regions hence one of the best Herschel targets for this work.

Lead Scientist: Jennifer Hatchell

Allocated time: 20.4 hours

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Cooling and chemistry in the most embedded massive protostars in the Magellanic Clouds

Stars form from contracting molecular cloud cores, but this process relies heavily on the ability of the core to cool and to overcome the magnetic barrier; this, in turn, depends on the chemical composition and could therefore lead to drastically different outcomes at low metallicity. However, most of what we know about star formation is derived from studies of solar-metallicity YSOs in the Milky Way. To investigate the role of metallicity on the star-formation process we propose to observe a sample of early-stage massive young stellar objects in the metal-poor Small and Large Magellanic Clouds. These were selected from among sources with spectroscopic evidence of ice and/or maser emission, and comprise a range in luminosity. We propose to use PACS and SPIRE FTS to measure the strengths of key atomic and molecular lines, in order to measure the temperature, density, ionization state and abundances of the main cooling species in these objects. By comparing the SMC and LMC samples, and Galactic samples of YSOs, we will assess the effect of the reduced metallicity on the formation process of massive stars.

Lead Scientist: Joana Oliveira

Allocated time: 34.6 hours

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A Herschel Survey of Disks across the Stellar/Substellar Boundary in Taurus

With the exceptional sensitivity of the Herschel Space Observatory, we propose to map a complete sample of 124 low mass members of the Taurus star-forming region, spanning the transition from low mass stars to brown dwarfs. Taurus is the ideal population for this investigation since the low stellar density enables the detailed study of individual objects without contamination from nearby sources. The sensitive PACS 70um and 160um maps of all sources will provide a census of disks, ranging from primordial gas rich disks to transition disks and debris disks, and define a benchmark population study for comparison with objects of higher mass, older ages, and in different environments. For the 59 targets with evidence of disk excesses from Spitzer 24um images, we also propose to obtain SPIRE 250-500um scans to further characterize the disk properties. The Herschel data for all sources will be combined with existing photometry to construct SEDs over the optical to submm range, and we will fit the SEDs with a comprehensive grid of models developed with the state-of-the-art radiative transfer code MCFOST. The proposed Herschel data cover wavelengths inaccessible from the ground and over the important range associated with the transition from optically thick to optically thin emission. By comparing the well-sampled SEDs with an extensive grid of models, we will estimate key structural parameters such as radius, mass, scale height, and evidence of flaring or dust settling. These properties represent important observational constraints on models for brown dwarf formation and the viability of these disks as sites for future planet formation.

Lead Scientist: Jenny Patience

Allocated time: 35 hours

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Characterizing the life cycle of interstellar matter in the Magellanic Clouds with CII and CI

The understanding of the processes governing the formation of interstellar clouds and subsequent star formation is key for our understanding of how galaxies evolve in our Universe. Special interest is given to the study of low-metallicity interstellar matter as it is thought to be representative of the environment where stars formed at earlier cosmological time. Unique targets for this study are the Large and Small Magellanic clouds, which are the closest low-metallicity star forming systems. We propose deep, velocity--resolved observations of the [CII] 158 um, [CI] 609um, and [CI] 370um lines towards 54 representative positions in the Large and Small Magellanic clouds with the HIFI instrument on board of Herschel. These will be combined with our MAGMA CO data to obtain a complete inventory of carbon in the Magellanic clouds. We selected positions to represent different ISM environments, based on whether they show: a) HI peaks with little or no 160um dust emission and no CO, b) HI and 160um peaks but still no CO, and c) CO peaks. We also include a sample of lines-of--sight observed by FUSE which have known H2 column densities, which will allow us to calibrate our use of [CII] as a tracer of HI and H2 column densities. Our sample therefore includes clouds in different stages of evolution going from diffuse atomic to diffuse molecular and to dense molecular clouds. We will use an excitation/radiative transfer code and a PDR model to derive the physical conditions of the line-emitting gas. Our observations have the potential to discover large quantities of dark H2 gas traced by [CII] and perhaps [CI] emission, as recently observed in [CII] emission in the galactic plane (Langer et al. 2010 and Velusamy et al. 2010).

Lead Scientist: Jorge Pineda

Allocated time: 59.6 hours

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Protostellar Envelopes Resolved Inside and Out: A Close Look in the Far-IR

We propose to use Herschel PACS and SPIRE observations to develop a detailed characterization of the envelope temperature and density structure in four nearby (d ~ 200-300 pc) protostars. This will enable us to understand how the non-axisymmetric structure in the surrounding dusty envelopes affects the infall process and the structure of the inner envelope. The goal of this proposal is to take advantage of the superb spatial resolution in the far-IR and sub-millimeter to constrain envelope densities and temperatures over the wide range of spatial scales involved in protostar formation. The proposed observations will resolve the warm inner envelope around these protostars with PACS and map the cold outer envelope with PACS and SPIRE with unparalleled sensitivity and resolution. The multi-band Herschel data enable us to construct dust temperature and density maps which we will combine with our existing Spitzer/near-IR dust extinction maps and measurements of envelope mass and morphology. We will interpret our observations using radiative transfer models to provide the most comprehensive characterizations of protostellar envelope density and temperature structures with which to confront theory.

Lead Scientist: John Tobin

Allocated time: 3 hours

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Outflows from evolved Class II sources: an Herschel/HIFI insight into the kinematical/physical properties of the atomic and molecular component.

Stellar jets are known to play a key role in the overall star formation process as they can remove angular momentum from the disk and disperse the parental envelope. A characteristic emission lines spectrum is produced by the shocks caused by the interaction of the ejected material with the surrounding medium. The collimated, fast and hot gas (T~2000-1e4 K) is traced by atomic and H2 lines, while the slow and cold swept-up material (T~10-20 K) can be probed through millimeter lines. Herschel opens a window on the "warm" component at 100-2000 K, which hold crucial information on the understanding of the connection between the outflow atomic and molecular components and the transfer of energy to the surrounding medium.

Preliminary results obtained from the analysis of GASPS/PACS data of Class II sources associated to jets detected at optical/NIR wavelengths show extended and velocity shifted emission in atomic ([OI]63um, [CII]157um) and molecular (CO, H2O) lines, suggesting that these lines are originating in the outflowing gas. However, also emission from the surrounding accretion disk may contribute to the emission in the unresolved star-disk region (PACS resolution ~9.4").

We propose to complement the GASPS/PACS data with HIFI observations of the [CII]157um, CO 10-9, and H2O at 556.9 GHz lines in a small sample of GASPS targets associated to outflowing gas sigantures. HIFI high spectral resolution (fraction of km/s) will allow us to observe line profiles and separate emission from the disk and the outflows. The [CII]157um line, with the [OI] lines detected by PACS, will probe the jet atomic component, while HIFI and PACS CO and H2O lines will allow us to derive kinematical/physical properties of the molecular component. The characterization of molecular gas component, as well as the estimates of the mass loss rate associated to the different component is crucial to test the magneto-hydrodinamical jet models and understand the interplay between accretion and ejection.

Lead Scientist: Linda Podio

Allocated time: 26 hours

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An in-depth Herschel study of gas, dust, and ices in FU Orionis objects

We propose to obtain the broad-band medium-resolution spectra of 15 known outbursting sources with Herschel PACS and SPIRE to cover the 50-650 micron range and to study both the continuum (and the spectral features of ices and dust) and the emission lines. Additional photometry with PACS and SPIRE will be obtained to better characterize the direct environment of the FU Orionis objects. The main goals are 1) to place the FU Ori objects in the context of young stellar evolution by looking for differences in infrared spectral diagnostics between FU Ori objects and regular young stars. To this end we plan 2) to study the composition and evolution of dust grains in FU Ori objects, 3) to look for the presence of ices, 4) to identify atomic lines, in particular faint lines not previously or barely identified with ISO and to use line ratios to constrain the emission mechanism, 5) to search for molecular lines of hydroxyl and water, and of high transition states of (J=13-30) of CO. The CO lines will be used to constrain the origin of the lines (outflow, disk), 6) to use the Herschel spectra and photometry with ground-based and Spitzer data to fit the spectral energy distributions with radiative transfer codes to derive the disk and envelope properties. The Herschel observations of our sample of outbursting sources will probe an important phase in the life of young stellar objects with the aim to better understand their differences and their common properties, and to better place them into the evolutionary sequence from Class I star to Class II stars.

Lead Scientist: Marc Audard

Allocated time: 31.3 hours

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Understanding the Protostellar Mass Accretion Process: Herschel 100-500 micron Photometry of Low Luminosity Embedded Protostars

Spitzer Space Telescope surveys of nearby, low-mass star-forming regions have discovered a new class of very low luminosity objects (VeLLOs), protostars embedded within dense cores with luminosities less than or equal to 0.1 Lsun. VeLLOs represent the extreme low end of the protostellar luminosity distribution, which is comprised mainly of sources below about 1 Lsun. The standard model of star formation, which predicts a mass accretion rate constant with time, is inconsistent with such a large population of low luminosity embedded protostars, leading numerous recent authors to suggest that mass accretion is variable and/or episodic in nature. Further constraints on this mass accretion process require far-IR and submm data to fill in the gap between existing Spitzer mid-IR and ground-based millimeter continuum data. We propose to obtain Herschel PACS and SPIRE 100-500 micron photometry of 24 confirmed and candidate embedded protostars with L < 1.0 Lsun. With these data, we will: (1) calculate accurate evolutionary indicators, (2) provide essential inputs for source models that seek to constrain the properties of both the protostars and the dense cores in which they are embedded, and (3) confirm or reject candidates that have not been conclusively shown to be embedded protostars. The proposed observations will provide crucial data for further understanding the protostellar luminosity distribution and mass accretion process for a very modest (6.0 hours) allocation of observing time.

Lead Scientist: Michael Dunham

Allocated time: 6 hours

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Diffuse ISM phases in the inner Galaxy

First HIFI and PACS observations obtained in the framework of the PRISMAS and HEXOS key programs have demonstrated the advantage of using absorption spectroscopy for studying the diffuse interstellar medium in the inner Galaxy. Detections of HF, OH+, H2O+, CH+, CH and the N-hydrides have significantly improved the knowledge of the diffuse molecular gas and started to open windows on the diffuse atomic gas. However the information on the diffuse ionized gas remains fragmentary. We propose to take advantage of the Herschel spectroscopic capabilities and further characterize the diffuse neutral and ionized interstellar medium along lines of sight already selected in the PRISMAS and HEXOS programs. We target the fine structure lines of ionized nitrogen and carbon, [NII] 1.46 THz, CII] 1.9 THz,and the ground state and first excited lines of neutral carbon at 492 GHz & 809 GHz. [NII] is tracing is diffuse ionized gas, while the neutral carbon lines reveal the diffuse neutral gas and probe the gas pressure and [CII] traces both the neutral and ionized matter . Towards strong far infrared sources such as our targets, we expect that the [CII] line profile will present a superposition of emission and absorption features, that can only be resolved by the high spectral resolution provided by HIFI. Even for [NII] and [CI], the profiles may show superpositions of absorption and emission features, justifying our request for HIFI spectra, since the gas and electron densities in the foreground material are much lower than in the background sources. We propose to take advantage of the sensitivity offered by absorption spectroscopy to determine the ionized carbon abundance with an unprecedented accuracy. The proposed observations will therefore bring new measurements of the abundances of neutral and ionized carbon abundances, neutral gas pressure, and ionized gas filling factor in the inner Galaxy that will provide a complete picture of the respective volume and mass filling factor of the ISM phases in the inner Galaxy

Lead Scientist: Maryvonne Gerin

Allocated time: 13 hours

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Kinematics and Chemistry in Ultracompact HII regions: the case of Mon R2.

Ultracompact HII regions are defined as regions of ionized gas with diameters smaller than 0.1 pc. Mon R2 is the only nearby Ultracompact HII region that can be resolved with Herschel. This source has already been observed and has been proved to host a dense photon-dominated region surrounding the Ultracompact HII region. For the simplicity of its geometry and the absence of shocks, this source is an excellent target to investigate the chemistry of extreme PDRs. Observations done with HIFI during the Prioritary Science Phase combined with previous observations from the IRAM 30m telescope permitted to constrain a simple scenario to describe this region: a dense PDR layer (n = 5x106 cm-3) surrounded by a lower density (n = 105 cm-3) UV protected envelope. We propose to do maps of tracers of the regions of the PDR close to the HII region in order to characterize its movement. At the same time, we propose to observe some hydrides molecules, which chemistry is poorly known in such regions. HIFI is a unique oportunity to study such hybrides with fine/hiperfine structures, due to its high resolution. That way, with only 3.4 hours of observation and some work in modeling and interpreting the results we would be able to characterize the kinematics and chemistry of this region, that can be used as a template of similar objects, like the surface layers of circumstellar disks and/or the nuclei of starburst galaxies.

Lead Scientist: Manuel Gonzalez

Allocated time: 3.4 hours

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First steps toward star formation: unveiling the atomic to molecular transition in the diffuse interstellar medium

We propose to map molecular material that is forming in the diffuse insterstellar gas, exploiting the unique capabilities of PACS and SPIRE: large area mapping at high angular resolution, sensitivity, and wavelength coverage spanning the peak of the dust spectral energy distribution. The main scientific goal is to discover the physical conditions in cirrus clouds that lead to the formation of the seeds of molecular clouds. Molecular hydrogen formation is fundamental to understanding the structure of molecular clouds and the core mass function (CMF) in the framework of the turbulent, magnetized and thermally bi-stable interstellar medium.

Our strategy is to map two regions at high Galactic latitude with PACS and SPIRE and use the dust opacity deduced from Herschel data to map the total column density of matter. Then using our high resolution 21-cm data for these fields, the atomic-correlated contribution can be removed, leaving a map dominated by dust in the molecular gas. Statistical properties of the molecular structures will be related to the properties of interstellar turbulence, thermal instability, and CMF seen in molecular clouds. The H I data are essential to this project, not only to uncover the molecular gas but also to probe the dynamical conditions in which the molecular gas has formed.

Both fields are part of a large project of H I observations of high Galactic latitude fields. The Spider field, a faint cirrus cloud with highly filamentary structure, is representative of the formation of H2 in dynamical conditions dominated by interstellar turbulence, with an average amount of molecular gas for diffuse clouds (estimated at about 15-20%). The Draco nebula, the archetype of interstellar matter re-entering the local interstellar medium after being expelled into the halo via the Galactic fountain, has a strikingly clumpy structure induced by its bulk motion with respect to the local ISM. There is a wide range of conditions to be modeled, including patchy CO emission.

 

Lead Scientist: Marc-Antoine Miville-Deschenes

Allocated time: 31.4 hours

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Probing the mechanical and radiative feedback from young stars in the molecular clump containing HH 1/2 and NGC 1999

We propose PACS spectroscopic observations in the line and range scan mode of the HH 1/2 jet, its driving source, and a nearby cloud cavity irradiated by a B9/A0 star in an intermediate-mass molecular clump in L1641. Our aim is to study the details of the mechanical and radiative feedback from new born stars on their immediate cloud environment and how it affects the structure, stability and star formation potential of the cloud clump from which they have formed. We will map the HH 1/2 outflow, and the newly discovered cavity in NGC 1999, in the far-infrared fine-structure lines of [C II] and [O I], and in several rotational lines of CO and H2O. From these observations we will spatially separate the various sources of energy and momentum, and place strong contraints on the density and temperature of the emitting gas. We will follow the spatial variations in the shock structure along the jet to probe the interaction of the jet with the surrounding molecular gas. By constraining the temperature and density of the surface walls of the cavity in NGC 1999 we will test if the temperature is high enough to represent photoevaporation, and estimate the rate of photoevaporation.

Lead Scientist: Manoj Puravankara

Allocated time: 13 hours

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ASCII: All Sky observations of Galactic CII

The Milky Way and other galaxies require a significant source of ongoing star formation fuel to explain their star formation histories. A new ubiquitous population of discrete, cold clouds have recently been discovered at the disk-halo interface of our Galaxy that could potentially provide this source of fuel. We propose to observe a small sample of these disk-halo clouds with HIFI to determine if the level of [CII] emission detected suggests they represent the cooling of warm clouds at the interface between the star forming disk and halo. These cooling clouds are predicted by simulations of warm clouds moving into the disk-halo interface region. We target 5 clouds in this proposal for which we have high resolution HI maps and can observe the densest core of the cloud. The results of our observations will also be used to interpret the surprisingly high detections of [CII] for low HI column density clouds in the Galactic Plane by the GOT C+ Key Program by extending the clouds probed to high latitude environments.

Lead Scientist: Mary Putman

Allocated time: 10 hours

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Hot CO in the Massive Star Forming Region DR21

We plan to resolve the detailed physical and dynamical structure of the massive star forming (SF) region DR21~C which has a prominent bipolar outflow visible in 2 micron emission of vibrationally excited H2, tracing hot, shocked gas. While, the shock is hardly affecting most of the molecular line emission of the region (Lane et al. 1990, Ossenkopf et al. 2010), only [CII] is showing an additional broad blue wing indicating that the [CII] emission is not only originating from that warm gas, but also from the ionized wind in the blister outflow. H2 and CO are at least partly co-existent and hence should show similar signs of shocks, but surprisingly 13CO(10-9) doesn't, so many question remains:

- Is there any CO that is directly affected by the shock and if so, at at which AV does the shock excitation stop? - Why does CO up to 10-9 show no direct signature of shock heating or outflowing material? - Does the shock only affect H_2 and ionized material? - Which volume of the source is affected/heated by the shock? - Which volume of the source is heated by the UV radiation from the cluster?

The aim of this proposal is to understand how shock/outflow and UV radiation from the embedded OB cluster contribute to the excitation of the surrounding material and where exactly the transition from shocked to unshocked material occurs.

Lead Scientist: Markus Röllig

Allocated time: 11.6 hours

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Characterizing the structure of an unusually cold high latitude cloud

We propose a PACS and SPIRE photometric observation at 100, 160, 250, 350 and 500 micron to study an unusually cold cloud detected by the BOOMERanG experiment at high galactic latitudes (b = -31 deg). This cloud has a temperature of T = 7 +- 3 K and this measurement is confirmed also by Planck-HFI data. Even if the temperature is so low, other properties are not that extreme: it has normal HI column density, gas-to dust ratio and no molecular material. A closer look at 100 micron shows, at 4' resolution, a wealth of brighter clumps embedded in the cloud that could be mostly molecular, hence hidden from the large beam HI and CO surveys. They can be pre-stellar cores and this would explain the low temperature. We propose to map a 30'x30' area centered on the cloud to study the substructure and the composition of that region. The observation with the Herschel angular resolution and band coverage will improve the knowledge of the early stages of star formation and of the structure and composition of the interstellar medium at tens of arcseconds angular scale. This is particularly interesting as the region is located at high latitudes, in an area that is supposed to be poor of star formation activity. With Herschel data we will be able to characterize the properties of the clumps and of the dust around, like temperature, spectral index, mass and density in order to better determine the physical processes occurring in this region and structure and substructures composition.

Lead Scientist: Marcella Veneziani

Allocated time: 6.8 hours

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HYSOVAR: Circumstellar Disks Variability around Young Stellar Objects in the Orion Nebula Cluster with Herschel/PACS

The variability of Young Stellar Objects (YSOs) have been demonstrated over half a century ago from optical observations. More recent time series photometry of YSOs in the thermal infrared have shown their great potential to probe the structure of inner circumstellar disks (r << 1 AU), in particular the presence of warps and `clouds' in the disks which may owe their existence to the gravitational torques from close-in planets. For instance the YSOVAR program used the Spitzer IRAC instrument to monitor over 1400~YSOs and establish that 70% of them show significant variability in the mid-IR. Today the Herschel/PACS spectral coverage, sensitivity and stability offer a unique opportunity to access the wavelength regime sensitive to the dust thermal emission from the terrestrial habitable zone through the ice-line where gas giants are expected to form. We propose the HYSOVAR program, an expansion of YSOVAR with the Herschel/PACS Photometer, to monitor the flux variations of 100+ Class I YSOs in Orion over weeks-to-years time scales. This small (9.9 hours) exploratory program would greatly increase the statistics and sensitivity of previous studies in the far-IR, and it would help us identify the physical processes responsible for the observed infrared variability by placing strong constraints on existing models of star and planet formation.

Lead Scientist: Nicolas Billot

Allocated time: 9.9 hours

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A Deeper Look at the 3-10 Myr Old Disks in the Orion OB1 Association

We propose to obtain deep 70/160 micron PACS Photometer observations of populations in the Orion OB1 association, spanning the critical 3 to 10 Myr range of ages when disks are supposed to dissipate and planets to form. Our ongoing large-scale survey of the Orion OB1 star-forming regions has allowed us to find the elusive low mass population in the older parts of the association, and secure the photometric and spectroscopic data to fully determine the stellar and accretion properties of these objects. We propose to obtain slow-speed scans of five 30'x30' fields, covering sections of the ~ 3 Myr old cluster sigma Ori, a ~ 5 Myr old group in the Ori OB1b subassociation, and the ~ 9 Myr old 25 Ori group, the most populous stellar group at this age within 500 pc. Our Spitzer IRAC and MIPS data for the proposed fields allow us to estimate that we will detect at least 62 disks in our PACS observations, 48% of which also have Spitzer IRS data. With the Herschel far-infrared fluxes and our mid-infrared and optical fluxes we will construct the most complete spectral energy distributions for a large sample of 3-10 Myr disks. The interpretation of these SEDs with our irradiated accretion disk codes, constrained by the stellar parameters and mass accretion rates determined independently from the UV excess, will allow the best characterization to date of disks in this age range, and provide essential constraints on theoretical models of disk evolution and planet formation.

Lead Scientist: Nuria Calvet

Allocated time: 39.6 hours

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Pillars of creation: physical origin and connection to star formation

Herschel SPIRE/PACS photometry observations performed within the HOBYS (Herschel imaging survey of OB Young Stellar objects) key program have revealed a wealth of interesting structures in high-mass star forming regions. The most spectacular of those are 'pillars' and 'globules'. These features -- partly known from Hubble Space telescope or Spitzer images -- are formed due to photoevaporation at the interface between a molecular cloud and an HII region, and are thus intimately linked to high-mass star formation. The process of how these pillars are created, and under which conditions low- or high-mass stars form within them, are not yet clear. Classical approaches (e.g. Rayleigh-Taylor) can not explain pillar formation, so we have embarked upon a dedicated project to fully simulate pillars and globules using the (magneto)-hydrodynamic code HERACLES that comprises gravity and ionization. The model is intended to be coupled with a radiative transfer photon dominated region code (KOSMA-tau).

We propose here to make use of the Herschel spectroscopy capacities to map/make single pointings, in a number of atomic and molecular lines, of selected pillars and globules in three different regions (Rosette, Cygnus, M16), spanning a large range in UV intensity and density. We intend to observe the important cooling lines of [CII] at 158 micron and [OI] at 63 and 145 micron with PACS, the [CI] finestructure lines at 370 and 609 micron and the mid-to high-J CO and HCO+ ladder with the SPIRE FTS. Spectrally resolved [CII] mapping with HIFI is also required to derive the velocity information. These observations will be compared to the large existing complementary data set for each source, to study the physics of pillars and will additionally serve as input for the models, to ultimately explain pillar formation and star formation within them.

Lead Scientist: Nicola Schneider

Allocated time: 31 hours

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Follow-up spectroscopy of two selected filaments found in the Herschel Gould Belt Survey: A turbulent shock origin ?

One of the early discoveries made with Herschel during the science demonstration phase is the fascinating omnipresence of filamentary structures in the cold interstellar medium and the apparently intimate relationship between the filaments and the formation process of prestellar cloud cores. Our first results from the Gould Belt survey in the Aquila Rift and Polaris Flare regions suggest a picture of core formation according to which filaments form first in the diffuse ISM, probably as a result of interstellar turbulence, and then prestellar cores arise from gravitational fragmentation of the densest filaments. To get further insight into the formation of prestellar cores, it is crucial to clarify the origin and nature of the filaments seen in the wide-field SPIRE/PACS images. Here, we propose follow-up observations of the central parts of two selected filaments with the SPIRE and PACS spectrometers to characterize the physical conditions of the gas and test the hypothesis that the filaments are formed behind low-velocity interstellar shock waves associated with the dissipation of turbulent energy. If this is indeed the case, we expect to detect a number of emission lines such as [CII] (at 158 microns) and [CI] (at 609 microns), and several high-J CO lines which are primary coolants of the postshock gas.

Lead Scientist: Philippe Andre

Allocated time: 58.3 hours

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Galactic Origins of Star Formation in the W43 Complex (GLOW)

Star formation is one of the most important processes in the universe, strongly influencing the evolution and structure of matter on all scales. Still the early phases are not totally understood. The progression from low density gas and dust to star forming cores still awaits a persistent description.

One model that aspires to explain molecular cloud formation is the "converging flows" model. The term refers to the convergence of HI streams that can naturally be driven by gas motion within Galactic arms. The theory of converging flows is the first one that can explain star formation self-consistently. It sets the stage for rapid dispersal (fragmentation into filamentary structures) of molecular clouds and explains naturally the observed short lifetimes of star forming stages which have, for long, been a problem.

We propose to map three parts of the giant molecular complex W43, that show examples of converging flows and filamentary structure in C+. This line is known to be a good tracer of the transitional phase between atomic and molecular gas, particularly the phase where the gas is already molecular, but CO has not formed yet. We strive to observe the selected targets with Herschels HIFI instrument, to obtain detailed spectral information. With the addition of large scale maps of 13CO, that we have taken with the IRAM 30m and JCMT, this will give us a coherent picture of the region, needed to investigate the fluctuation of the molecular gas and compare these results to the theoretical models of converging flows.

The main scientific questions of this project are: (a) How do colliding flows of molecular gas form and how do they form filamentary structures? (b) How do these flows affect the formation of dense cores and thus accelerate star formation? The results of this proposal, complemented by other projects, will give deep insight into unknown mechanisms of star formation and, beyond that, pave the way to follow-up observations with Herschel and other observatories.

Lead Scientist: Philipp Carlhoff

Allocated time: 10 hours

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Molecular Oxygen in Orion

Observations carried out to date for the Herschel Oxygen Project (HOP) indicate that the abundance of a potentially major oxygen-bearing species, O2 (molecular oxygen), predicted to be as high as 1e-4, is less than 1e-7. One extremely interesting exception is Orion. We have 2 hours of integration on the 487 Ghz and 774 GHz O2 transitions, and see statistically significant emission in two velocity features, at ~ 6 km/s and ~ 12 km/s. These data were taken at the Peak 1 position of strong H2 vibrational emission, approximately 40" from the KL/hot core position. Plambeck and Wright (1987) found that the Peak A position near the hot core is a strong source of HDO emission at ~12 km/s. Since HDO is thought to be released from recently warmed grains, this may be intimately connected with the low O2 abundance being a result of atomic oxygen being frozen on cold grains and hydrogenated to water ice. When released after grain heating, it produces a significant gas-phase abundance of water and molecular oxygen. The HOP project did not include the KL/hot core position (Peak A is within 5") due to concerns about line confusion. However, data from the HEXOS survey confirms that the the O2 lines are in relatively windows, and shows O2 emission at the same 6 km/s and 12 km/s velocities. The line intensities are a factor ~ 5 stronger than at the H2 Peak 1 position, although noise is very large due to limited integration time. This suggests that the emission is from the hot core (6 km/s) and Peak A (12 km/s). We thus request 12 hours of time to carry out deep integrations at the frequencies of the 487, 774, and 1121 GHz, O2 lines, pointing at a position that includes the hot core and Peak A. This will confirm the identification as molecular oxygen (with three transitions at matching pair of velocities) and give a good handle on the temperature of the region producing O2 emission and its total column density. The total time requested is 12.1 hours.

Lead Scientist: Paul Goldsmith

Allocated time: 12.1 hours

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The Structure of a Molecular Cloud Boundary

Molecular clouds do not exist in a vacuum, but are embedded in a warm, diffuse interstellar medium containing hydrogen largely in atomic form, and ionized carbon. Based on theoretical modeling, dense, cold clouds are surrounded by an intermediate temperature envelope in which the hydrogen is molecular (due to efficient self-shielding) and in which carbon changes from ionized to atomic, to molecular (primarily CO) as one moves to regions of greater extinction. This cloud envelope is expected to have a major impact on the structure of dense cloud in which star formationtakes place, as it can add to the pressure support confining them, and can serve as a conduit for energy flowing into the molecular cloud that can be critical for sustaining observed turbulence. This boundary layer is not readily observable in CO since the abundance of this species has dropped dramatically, and it is also difficult to study in molecular hydrogen emission, as the temperature is too low to significantly populate even the lowest excited rotational states. The boundary, sometimes called "dark gas", possibly contains a significant fraction of the total mass of the dense ISM. Based on detection of weak H2 emission from the boundary of the Taurus molecular cloud by Goldsmith et al. (2010), we here propose to use the unique capabilities of Herschel to make a well-calibrated cut through the "linear edge" boundary region in Taurus in the 158 micron fine structure line of CII, and both the 492 GHz and 810 GHz fine structure lines of CI. Accurate calibration is essential and cannot be achieved using ground-based facilities. We propose to use the HIFI instrument to resolve the line widths and probe the kinematics in the boundary layer. The ratio of the CI lines yields the density, and these lines, together with the distribution of intensity of CII and H2 will allow us to develop a well-defined model for the boundary layer. This will address important questions about molecular cloud structure, total mass, and evolution.

Lead Scientist: Paul Goldsmith

Allocated time: 17.3 hours

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The Auriga-California Molecular Cloud: A Massive Nearby Cloud With Powerful Diagnostics For Early Stages of Star Formation

We propose to map the Auriga-California Molecular Cloud (AMC) with the same observing parameters as being used for the rest of the clouds in the Gould Belt by the Herschel GT team conducting that program. The AMC was not included in that program BUT is extremely important as a counterpoint to the Orion Molecular Cloud (OMC) because it is as large and massive as the OMC but has a factor of 10 lower level of star formation, most of which is concentrated at the southeast end near the LkHalpha 101 cluster. We already have complete Spitzer survey data on this cloud and are in the process of obtaining JCMT line and continuum survey observations. The OMC has informed our understanding of star clusters and massive star formation. It is essential, however, to test that understanding by observing other massive clouds with differing levels of star formation. The combination of Herschel data with our existing Spitzer and molecular line data is vital to understand the physical reasons underlying the large differences in star formation between these two regions. Herschel's combination of angular resolution and 5-band imaging for dust temperature and emissivity measurements permit a uniquely high level of analysis of the far-IR emission from the AMC and comparison with the OMC.

Lead Scientist: Paul Harvey

Allocated time: 19.1 hours

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The chemistry of nitrogen in dark clouds

Nitrogen is the fifth most abundant element in the local Universe. It is essential component of molecules associated to Earth-type life. Yet, the reservoir of nitrogen in the dense ISM, where stars, and ultimately planets, form, is not known. This is for good reasons. The main reservoir of gas-phase nitrogen are expected to be N or N2, and it is likely that most of the nitrogen be indeed frozen-out on dust grains in the form of ammonia ices. However, N and N2 are not observable in the shielded environments characterizing the embryos of star-forming regions. Hence, all what is know about nitrogen must rely on indirect observations of N-bearing molecules, the lightest (and thus among the easiest to form) of which are hardly detectable from the ground. To date, and despite longstanding efforts, our comprehension of the chemistry of nitrogen remains elusive. The HSO/HIFI instrument is opening new avenues in this respect, allowing astronomers to readily detect nitrogen hydrides and several key species of the nitrogen chemistry. This is the aim of this proposal. We propose the observation of key species that are observable only with Herschel. Those include NH, NH2 and NH3 (in their ortho and para forms), as well as their deuterated isotopologues, and other pivotal species like CH and CH2. This corpus of observations in order will allow to assess our understanding of the chemistry of nitrogen in dark cloud conditions, and answer the fundamental and open question, whether dust processes are necessary catalysts in this chemistry.

Lead Scientist: Pierre Hily-Blant

Allocated time: 29.4 hours

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High-J lines of HCN as tracer of feedback processes in high-mass star formation

The mechanisms involved in the formation of massive stars, and particularly the process of feedback from already-formed stars, are not well understood. Recent models of star formation have started to investigate the role of mechanic (outflows) and radiative feedback, but observational evidence for these processes altering the star formation process has been lacking. In an analysis of the HEXOS data, we have found that high-J HCN lines are perfectly suited to study this phenomenon: in SgrB2(M), they show a reversal of the infall profile at high J, indicating that in the inner regions the onset of feedback is halting the inflow, and the gas is actually expanding again.

In this proposal, we want to apply this powerful technique to a sample of high-mass star-forming cores at similar stages of development as SgrB2(M).

Lead Scientist: Peter Schilke

Allocated time: 16 hours

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Luminosity and mass loss history of the high-mass protostar IRAS20126+4104

The main goal of this project is to estimate the luminosity of the high-mass protostar IRAS20126+4104 and obtain a direct measurement of the mass loss rate of the associated bipolar outflow. This is a well studied object, where a 7 Msun protostar is surrounded by a Keplerian disk and powers a bipolar outflow. The relatively small distance (1.64 kpc) and the limited complexity of the surroundings of this object, combined with the unique angular resolution of HERSCHEL in the far-IR, make it possible to reconstruct the spectral energy distribution and thus obtain an accurate estimate of the stellar luminosity. Knowledge of the mass and luminosity will set constraints on the evolutionary stage of the young stellar object. We also want to observe the OI 63 micron line which is strictly related to the mass los rate of the outflow. The latter can thus be obtained independent of the usual drawbacks (uncertain molecular abundance, unknown outflow inclination angle) of the estimates obtained from CO and other typical outflow tracers. Moreover, since the outflow is precessing, one can also relate the position along the outflow with the time of ejection and reconstruct the mass loss rate history of this object. We will also observe the OI 145 micron line to verify possible opacity effects in the 63 micron line, from the ratio between the two lines. These data will be complemented with observations of the CI line to image possible photo dissociation regions, plus a number of CO lines observed with SPIRE, PACS, and HIFI, to reconstruct the excitation structure of the outflow, both in space and velocity.

Lead Scientist: Riccardo Cesaroni

Allocated time: 11.5 hours

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A Herschel SPIRE/PACS Imaging Survey of the MonR2 and CepOB3 Molecular Clouds

We propose complete surveys of the MonR2 (830 pc) and CepOB3 (700 pc) molecular clouds with SPIRE and PACS on Herschel to complement extant surveys with NEWFIRM and Spitzer at near-IR and mid-IR wavelengths, respectively. These two clouds complement cloud surveys of Orion and the Gould Belt clouds, as they are actively forming both low and high mass stars, and they are found at different evolutionary states relative to Orion. They are also closer to the galactic plane than Orion, implying a higher density of background stars and more reliable extinction maps. This study will impact our knowledge of two essential problems in star formation: the physical factors which determine the star formation rate and the initial mass function. We will produce high resolution maps of the large-scale dust column density and temperature from the SPIRE data maps and compare these to the density of protostars to determine the rate of star formation per area relative to the gas column density. We will use this data to reconcile inconsistent star formation rate vs gas column density correlations recently reported in the literature by measuring this relationship by independent means in a single cloud. To study the IMF, and its possible dependence on environment, we will look at factors that may determine the IMF: the mass of the pre-stellar core and the protostellar luminosity (which has a significant contribution from accretion). Pre-stellar cores will be extracted and characterized in terms of structure and mass. By combining the protostellar SEDs from Spitzer with PACS photometry, particularly 70um, better characterization of protostar bolometric luminosity and temperature distributions can be produced and compared among the clouds observed. With this data, we can examine how the core mass function and protostellar luminosity function can vary with density of young stars and cores and with the local conditions of the molecular gas, and how these vary from cloud to cloud.

Lead Scientist: Rob Gutermuth

Allocated time: 41.3 hours

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PACS and SPIRE observations of Galactic anomalous emission sources.

Despite the increasing evidence that the anomalous emission is a new physical mechanism acting in the diffuse interstellar medium, the nature and distribution of this component remains elusive. The currently most favored models attribute the observed microwave excess to rotating very small dust grains (PAHs and VSGs). Nonetheless, the infrared properties of the sources which, to date, are known to exhibit this type of emission are very poorly known mostly due to the limited angular resolution and frequency coverage of DIRBE and IRAS data.

We propose HERSCHEL PACS and SPIRE mapping of three Galactic anomalous emission sources (LDN 1780, LDN 675 and LDN 1111). This data, when combined with ancillary NIR and mid-IR data of comparable angular resolution (mainly from Spitzer), and coupled with available dust models, will allow to set tight constraints on the radiation field in the emitting sources as well as in their immediate surroundings. Such constraints, in turn, will allow to estimate the abundances of PAHs, VSGs and BGs, hence to shed light on the potential link between these dust populations and the observed microwave excess.

Lead Scientist: Roberta Paladini

Allocated time: 13 hours

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HIFI Observations of the C18O and C17O J = 5-4 to 15-14 Transitions in Hot Cores: A Direct Method to Obtain Total Column Densities

Using CO to trace the total H2 column density in molecular clouds is a common practice. This practice, however, can be fraught with difficulties. First of all, CO is often optically thick, especially towards the highest column density regions in molecular clouds (where stars are born) and so the analysis of CO emission requires complicated radiative transfer modelling. Second, the conversion from CO to H2 relies on an often unknown conversion factor and so a canonical value of 1:10,000 is usually assumed. This is especially problematic in cold (T < 20 K) dense gas, in which CO can be depleted onto dust grains. However, in warm gas surrounding massive or even low mass protostars (so called "hot cores''), depletion can be circumvented and the rarer isotopologues (13CO, C18O and C17O) are optically thin enough that they can be used as column density tracers.

We propose to use Herschel/HIFI to directly derive total C18O and C17O column densities in a number of high mass protostars. The method we will use offers an unprecedented opportunity to derive this fundamental quantity in a model independent fashion. The basic idea is simple. For an optically thin line the observed integrated emission is proportional to the column density in the upper state. This quantity can be derived without any assumptions regarding density or temperature. If you observe enough transitions of C18O one can simply estimate the total column from summing all the observed states and correcting for the missing population. In high mass star forming regions, the high densities and temperatures mean that the higher-J states can be significantly populated and an estimate of the total column density based on only a few low energy transitions can be seriously in error. With HIFI, we have access to > 7 high-J C18O transitions, and therefore we can calculate the total C18O column densities with great accuracy.

Lead Scientist: Rene Plume

Allocated time: 35 hours

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Water emission from outflows and hot cores in the Cygnus X proto-stars

The impressive first results from the WISH GT key program by van Dishoeck et al. indicate that water emission is bright towards the embedded proto-stars of all masses. These emissions are tracing outflows and warm inner regions of the collapsing envelopes (radiatively heated hot cores) which are unique probes of the cooling of these regions and of the kinematics of the dense warm gas. But WISH is limited by the reduced number of targets, and by the unavoidable biases introduced by the stringent selection of sources. The intermediate to high mass range is critical to challenge protostellar evolution models, and we argue that water emission from a complete sample of proto-stars in this mass range will be an important piece of knowledge for outflows to trace indirectly accretion and for hot cores to follow their time of appearance. Only Cygnus X is nearby and rich enough to provide a large sample of such proto-stars. We propose here to dramatically change the level of significance of WISH results by observing as many as 92 proto-stars covering the (final stellar) mass range of 3 to 20 Msun in the single complex of Cygnus X.

Lead Scientist: Sylvain Bontemps

Allocated time: 36.2 hours

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Synchrotron Radiation in Stellar Flares

Stellar flares emit copious radiation at X-ray, optical and radio wavelengths but have not yet been investigated in the far-infrared. Recent observations at millimeter wavelengths provide tantalizing evidence that a population of ultrarelativistic electrons may be accelerated during flares and may provide significant synchrotron radiation in the far-infrared and sub-millimeter wavelength regimes. Herschel observations of two very active stars with a history of strong, frequent and energetic flares will probe this wavelength regime for the first time. Ultrarelativistic electrons may hold the key to explaining the photospheric flare heating that is necessary to produce the observed white light flare emission which carries more than half of the total flare energy. Our team brings together experts in stellar flare optical and radio observations, particle acceleration and plasma physics, and radiative hydrodynamical atmosphere modeling. We propose to carry out a Herschel flare observing campaign together with several ground-based optical and radio observatories and to produce a new generation of flare models that include the ultrarelativistic electron population.

Lead Scientist: Suzanne Hawley

Allocated time: 30 hours

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Hi-GAL360: the crucial step toward a global understanding of star formation in the Milky Way

Hi-GAL360 will use PACS and SPIRE in parallel mode to obtain a 5-band photometric survey of the Outer Galactic Plane (OGP, beyond the solar circle) in the longitude range complementary to the Hi-GAL Open Time KP, i.e., 68° < l < 288° in a 2°-wide strip in latitude following the mid-plane of emission.

Hi-GAL360 data will enable a complete census of temperature, mass, density, column density and luminosity of filaments, clumps, and cores in the less confused outer Galaxy, where the assembly of filamentary structures and clouds and their fragmentation into clumps and cores can be uniquely characterised in low-metallicity and HI-dominated environments that are so different with respect to the inner Galaxy.

A complete OGP survey is required to obtain a statistically significant sampling of Galactic diversity - the full range of spiral arm, inter-arm, dust cloud, and star formation region properties - avoiding biases introduced by the study of specific or limited regions.

Hi-GAL360, together with Hi-GAL, will chart the Star Formation Rate and Efficiency from the Galactic Center to the far outer Galaxy, mapping the location and properties of star formation thresholds, thus providing the much needed connection between global scaling laws and the diversity of physical processes at work in the Galaxy. It will lay the foundations for a predictive, quantitative model of how star formation is triggered and regulated on all scales in the Milky Way. Such a model is vital to a full understanding of galaxy formation and evolution.

The merged Hi-GAL360/Hi-GAL `Atlas of the Galaxy' will provide essential `ground truth' for the interpretation of Herschel data on other galaxies from the Local Group to the high-redshift Universe where these objects are blended, and it will be the Herschel legacy that will remain unsurpassed for decades as the definitive survey of far-IR emission from the Galaxy.

Given our demonstrated community-oriented approach, we again waive our proprietary period.

Lead Scientist: Sergio Molinari

Allocated time: 276.8 hours

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Measuring Emissivity Indices of Dust in Dense Cores with the SPIRE/FTS

Maps of the thermal emission from dust in nearby star-forming regions have revealed an apparent similarity between the mass distributions of dense cores (CMF) and the stellar initial mass function (IMF). However, deriving the mass of a core from measurements of dust emission is not straightforward. The primary difficulty comes from uncertainty in the dust emissivity, and in particular the slope of the dust emissivity at long wavelengths (the emissivity spectral index). Ground-based observations of the continuum emission from cores suffer from atmospheric contamination, so the best way to derive the emissivity spectral index is from space-based observations. Here we propose to use SPIRE/FTS to map the spectral energy distribution (SED) in a sample of dense cores and constrain the emissivity spectral index of the dust emission. These observations will be supplemented with GBT ammonia observations to break the degeneracy between temperature and the emissivity spectral index inherent in SED fits. We will then be able to derive much more accurate core masses, test the similarity between the CMF and the IMF, and search for variations of the dust properties with environmental factors such as temperature and density.

Lead Scientist: Scott Schnee

Allocated time: 6.2 hours

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WATCH - WATer Chemistry with Herschel

Water is one of the most abundant species in star-forming regions and plays important roles in both the energy balance, acting as a coolant, and the chemistry of star formation. Many of the species involved in the water chemistry emit in the far-infrared and are thus not observable from ground based facilities because of atmospheric absorption. Therefore, the Herschel Space Observatory provides a unique opportunity to study the chemical reactions involved in the formation and destruction of water and to probe the energetic processes in star-forming regions. Previous results from Herschel have shown that two species, OH+ and H2O+, that were thought to be important in the water chemistry of young stellar objects, are now mainly attributed to foreground clouds. These results raised the question on which chemical paths the formation and destruction of water takes place in the interior of protostellar envelopes. In this proposal, we plan to observe the different formation and destruction routes of water in a sample of eight nearby young stellar objects, which were chosen to cover a broad range of masses, luminosities and evolutionary stages. We propose to observe H3O+ and HCO+, two species that are closely linked to the formation and destruction of H2O and require high temperatures for excitation, in serveral high-J lines. This effort is complementary to the observations of H2O and OH done in the 'Water in star-forming regions with Herschel (WISH)' key project. The combination of the information from the H2O, OH, H3O+ and HCO+ emission will tell us on which routes the formation and destruction of H2O in protostellar envelopes proceeds.

Lead Scientist: Susanne Wampfler

Allocated time: 19.4 hours

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Unraveling the Mysteries of Complex Interstellar Organic Chemistry using HIFI Line Surveys

We propose HIFI spectral line surveys of interstellar clouds to probe the influence of physical environment on molecular complexity. We will observe a statistically-significant sample of sources, cover a range of physical environments, and target selected frequency windows containing transitions from several known complex organic molecules. The goal of these observations is to correlate the relative abundances of organic molecules with the physical properties of the source (i.e. temperature, density, age, dynamics, etc.). Our broader research goal is to improve astrochemical models to the point where accurate predictions of complex molecular inventory can be made based on a given source's physical and chemical environment. The information gained from our proposed Herschel observations will serve as a benchmark for these astrochemical models and holds the promise of significantly advancing our understanding of interstellar chemical processes.

Lead Scientist: Susanna Widicus Weaver

Allocated time: 42 hours

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Probing the HH111 Molecular Outflow with Herschel

Outflows play a crucial role in star formation, since they carry away angular momentum from the protostars that drive them, allowing accretion to continue and the protostars to grow. They also represent a fossil record of the mass loss from their young hosts, providing valuable insights to the processes that govern accretion and outflow. Though jets and molecular outflows have been the subject of much scrutiny, the mechanisms responsible for launching and collimating the gas are still unclear and the relationship between the narrow optical jets and larger molecular outflows they accompany has still to be determined.

In order to understand the vital role of outflows in star formation, a detailed characterization of their physical, chemical and kinematical properties is essential. Accurate values for the mass, mass transport rate and momentum in outflows can then be derived to test competing formation scenarios, and the shock conditions can be determined. The HH111 jet and associated molecular outflow and CO bullets represent an excellent prototype of these outflow phenomena in which to accomplish this. We therefore propose to obtain a complete physical, chemical and kinematical picture of the hot molecular gas in the HH111 jet with Herschel by performing HIFI observations of selected CO rotational lines, SPIRE FTS mapping spectroscopy of the outflow region and SPIRE and PACS photometric maps of the same region. Together, these observations will enable a comprehensive study of the molecular gas and dust contained in the HH111 outflow, allowing an unparalleled determination of its physical properties and the role it plays in the mass loss from the central protostar. This, in turn, will give key insights into the mechanisms that power outflow phenomena in general.

Lead Scientist: Tom Bell

Allocated time: 17.4 hours

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Probing The Unique Environment Around Sgr A*

We propose to study the extreme conditions in the molecular gas surrounding Sgr A* by obtaining a full spectral survey of this source with Herschel/HIFI. This will provide a complete chemical inventory, containing multiple transitions spanning a broad range of excitation conditions, and will constitute a unique resource with which to explore the diverse physical processes at work and confront current models with important new constraints. The molecular gas in this circumnuclear disk also serves as a template for the study of central regions of other galaxies, helping to elucidate the properties in those distant sources. These data will also include absorption lines from many important hydrides in diffuse clouds along the line of sight, and we will also perform deep integrations at specific frequencies to target key metal hydrides, which will allow depletion, diffuse cloud chemistry and key chemical reactions to be probed. The plethora of emission and absorption lines that these observations will provide, across a frequency range that is largely inaccessible from the ground, will constitute a detailed chemical and physical portrait of the interstellar medium under a diverse and extreme range of conditions. As such, the proposed spectral survey and deep integrations represent a valuable legacy dataset for the future.

Lead Scientist: Tom Bell

Allocated time: 40 hours

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Extinction towards the Galactic Center

We want to use far infrared hydrogen recombination lines for 6.7 hours from the Galactic Center with Herschel/PACS. We then combine the far infrared measurements with existing near and mid infrared measurements of hydrogen lines for obtaining the differential extinctions between the lines. Above 100 microns the extinction is below 0.05 mag such that be obtain the absolute extinction over the full infrared.

Firstly the absolute extinction can be used for following goals:

Many of the bright stars in the Galactic Center are massive, young O- or WR-stars. Their stellar types and ages have been derived individually by means of atmosphere modeling.

Putting a reliable, absolute magnitude scale to the near infrared emission from Sgr~A* allows one to relate properly radio, submm, near infrared and X-ray data with each other.

The 'red-clump' feature in the HR-diagram is well visible for the Galactic Center stars. Its apparent magnitude combined with the extinction measures the distance to the Galactic Center, R_0, independent from other methods.

Secondly the extinction law in the whole infrared regime can be used for testing the surprisingly flat extinction law in the mid infrared found by previous work constraining. This extinction law can then constrain dust grain modells.

Lead Scientist: Tobias Fritz

Allocated time: 6.7 hours

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FIR study of dust processing in the Carina region

We propose to study dust processing and search for a signature of dust properties associated with massive star formation in a region of the Carina nebula, where a clear variation has been found by mid-infrared spectroscopy. ISO/SWS and Spitzer/IRS observations indicate the presence and variation of the feature around 22 micron in an interface region between the ionized gas and molecular cloud in the Carina nebula. The feature appears to be strongest around the ionization front and significant dust processing is indicated to take place. We propose to study this highly interesting region by PACS SED and line spectroscopy modes and SPIRE spectroscopy. We investigate the variation in the dust size distribution and degree of coagulation and search for possible features associated with the massive star-forming region. The present observation will provide the systematic far-infrared data of the region where clear evidence of dust processing is indicated for the first time and give crucial information on the study of material evolution in the interstellar medium.

Lead Scientist: Takashi Onaka

Allocated time: 13.1 hours

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Depletion and Deuteration of Ammonia in Pre-stellar Cores

Molecular line studies of dense cores have shown that NH3 is an excellent tracer of pre-stellar gas, which is the earliest phase in the formation of stars. Unlike most other molecules (mainly CO), ammonia does not deplete out in dense cores. This apparent non-depletion is still a mystery. To make matters worse, ammonia abundance has been shown to increase at the highest densities. The answer might lie in the choice of ammonia transitions that have been observed to propose non-depletion. These are the para-NH3 23 GHz rotational transitions that have critical densities of ~ 10^4 cm^-3 while NH_3 depletion is expected to occur at densities two orders of magnitude higher! However, the NH3 ground state transition at 572.5 GHz observable with Herschel has a critical density few orders of magnitude higher, close to where we expect to see depletion. We propose to unravel the ``seeming'' ammonia non-depletion in dense cores by mapping the densest region of a pre-stellar core (with heavy CO depletion) in ammonia. The molecular depletion is closely linked to molecular deuteration. NH2D is expected to be abundant in cold regions with significant CO depletion. The D/H ratio derived from the ratio of NH3 and NH2D column densities is consistently higher than that derived from other molecules, most importantly N2H+. The discrepancy is worse for higher mass cores where NH2D/NH3 ratios of up to 0.8 have been found! While other astrochemical processes may be at play, one of the prime suspects is again the poor choice of para-NH3 (1,1) transitions as dense gas tracer. We believe that this leads to ammonia column densities being underestimate. Here, we propose to observe NH3 J_K= 1_0-0_0 toward a high mass core where very high deuteration ratio has been found and derive the "true" NH3 column density. This proposal will address two fundamental issues with our understanding of ammonia chemistry in dense cores, (i) the seeming ammonia non-depletion and (ii) very high ammonia deuteration.

Lead Scientist: Thushara Pillai

Allocated time: 2.6 hours

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Under pressure: Revealing the thermal and spatial structure of strongly irradiated clouds in the Carina Nebula, the nearest laboratory of massive star feedback

The Carina Nebula contains some of the most massive and luminous stars in our Galaxy and is the best site to study in detail the physics of violent massive star formation and the resulting feedback effects, i.e.~cloud dispersal and triggering of star formation. We are engaged in a comprehensive multi-wavelength study of the Carina Nebula. Our new X-ray and near-infrared data, and mid-infrared data reveal and characterize the full stellar population. We also have used LABOCA at the APEX telescope to obtain a wide-field sub-mm map of the Carina Nebula; while it shows the morphology of the cold clouds in unprecedented detail, these single wavelength data do not permit to determine cloud temperatures, and thus cloud column densities and masses. Here we ask for 7.2 hours SPIRE/PACS time to map the full spatial extent of the clouds (5.4 square-deg.) simultaneously at 5 wavelengths. The HERSCHEL maps will yield fluxes at the critical far-IR wavelengths and allow us to reliably determine cloud temperatures, column densities, and thus cloud masses. This will yield a complete inventory of all individual clouds in the complex, down to cloud masses of 1 Msun, and allow us to detect the youngest and most deeply embedded protostars (down to 0.1 Msun). We will map large-scale temperature gradients and changes in the dust properties that are expected as a consequence of the strong feedback by the massive stars, and establish and compare the clump mass functions in different parts of the complex. By comparison with similar HERSCHEL data for other star forming regions, we can address the question of how the particularly high levels of massive star feedback influence the evolution of the clouds and the star formation process. These HERSCHEL data will also reveal the small-scale structure of the irradiated clouds and allow a meaningful comparison to our dedicated numerical simulations of the disruption of molecular clouds, the origin of the observed pillar-like structures, and the triggering of new stellar generations.

Lead Scientist: Thomas Preibisch

Allocated time: 6.9 hours

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Structure of translucent clouds observed with HIFI [CII] 1.9THz and in H2 in absorption by FUSE

We propose HIFI observations of 1.9 THz (158 micron) [CII] line emission in selected 27 lines of sight (LOSs) which have been observed in H2 absorption in UV by FUSE, and three observed in [CII ]2325A absorption by STIS. [CII] observations provide a powerful probe of warm diffuse clouds, and [CII] is a useful as a tracer of their warm H2 content. By combining FUSE and STIS which directly detects H2 and C+ in absorption and the HIFI [CII] data we can better constrain many of the physical conditions in the cloud including the density and pressure of the C+ gas. The [CII] line emission spectra will be complimentary to those observed in absorption in UV and, in addition to its extremely high velocity resolution, help us resolve the narrow absorption features in the H2 and HI gas. A comparison of the molecular H2 column densities inferred from the 1.9THz [CII] line in the clouds along the FUSE/STIS LOS with those directly measured by them will validate the interpretation of the HIFI [CII] emission observed by larger scale Galactic surveys. We request 22.7 hrs of observing time on HIFI in band 7b.

Lead Scientist: Thangasamy Velusamy

Allocated time: 22.7 hours

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HIFI studies of the small-scale structures in the Galactic diffuse clouds with [CII] and [CI]

The 1.9 THz [CII] observations provide a powerful probe of warm diffuse clouds, because they can observe them in emission and are useful as a tracer of their molecular H2 not directly traced by CO or other means. HIFI observations of [CII] provide a high resolution of 12 arcsec, better than that for single dish CO (> 30 arcsec) maps, and much better than HI (>30 arcsec). Thus with HIFI we have an opportunity probe the small scale structures in diffuse clouds in the inner Galaxy at distances > 3 kpc. To study the structure of diffuse ISM gas at small scales we propose HIFI maps of 1.9 THz (158 micron) [CII] line emission in a selection of 16 lines of sight (LOSs) towards the inner Galaxy, which are also being observed as part of the GOT C+ survey of [CII] in the Galactic plane. GOT C+ provides mainly single point spectra without any spatial data. Maps of [CII] will constrain better the cloud properties and models when combining [CII] and HI data. The proposed OTF X map will be along the longitude and latitude centered on 18 selected GOT C+ LOS over a length of 3 arcmin in each direction, which is adequate enough to provide sufficient spatial information on the small scale structures at larger distances (>3 kpc) and to characterize the CII filling factor in the larger beams of the ancillary (HI, CO, and CI data). The [CI] 609 & 370micron and the 12CO(7-6) (which lies within the CI band) are excellent diagnostics of the physical conditions of transition clouds and PDRs. We will use the ratio of the [CI] lines to constrain the kinetic temperature and volume density of the CII/CI/CO transition zones in molecular clouds using radiative transfer codes. We also propose OTF X maps in both the [CI] lines for all CII target LOSs. We anticipate fully resolved structural data in [CII] on at least 300 velocity resolved clouds along with their [CI] emissions. We request a total of 33.2 hrs of HIFI observing time.

Lead Scientist: Thangasamy Velusamy

Allocated time: 33.2 hours

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The origin of H2O+ in dense clouds

We try to resolve the chemical evolution of oxygen hydrides in radiatively heated dense clouds. This involves in particular H2O+ and chemically related species, which are formed by gas-phase reactions initiated by cosmic ray ionization in diffuse clouds, but may be predominantly produced by the evaporation of icy grain mantles and the subsequent ionization of water by UV radiation in heated dense clouds. We will investigate the full chain of species OH+, H2O+, H3O+, OH, and H2O, connected by gas phase reactions, to quantify the contribution of ice evaporation in dense clouds.

We propose to observe these species in the dense layers known to exist in two massive star-forming regions, DR21(C), where indications of H2O+ from hot gas were already found and where the hot layer is affected both by UV radiation and a strong shock from a bipolar outflow, and Mon R2, a PDR with similar parameters but no indications of shock processing of the hot layer.

Differences between the results from the two sources will provide an estimate for the impact of shocks on the H2O+ production. By comparing the observed abundances of OH+, H2O+, H3O+, OH, and H2O with steady-state PDR models, we will be able to quantify the amount of water that is fed into the gas phase by the evaporation or photodesorption of ice mantles from dust grains.

Lead Scientist: Volker Ossenkopf

Allocated time: 18.1 hours

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Open Time (Round 2)


Herschel Spectroscopy of Spitzer's Extended Green Objects: Tracing the Earliest Stages of Massive Star Formation

Massive star formation remains a poorly understood phenomenon, largely due to the difficulty of identifying and studying massive young stellar objects (MYSOs) in the crucial early active accretion and outflow phase. Large-scale Spitzer surveys of the Galactic Plane have yielded a promising new sample of young MYSOs with outflows, which are likely actively accreting: based on their extended 4.5 um emission in Spitzer images, these sources are known as "Extended Green Objects (EGOs)" from the common coding of three-color IRAC images. Extensive ground-based follow up observations revealed that the EGOs are indeed related to massive outflows from young systems with very high accretion rates (10^-3 Msun/year). They also revealed a wide variety of properties: some MYSOs appear in clusters, others are isolated, some are molecular line rich, others not. To test the hypothesis that these differences reflect evolutionary effects, we propose SPIRE/FTS and HIFI observations of 4 EGOs. SPIRE/FTS spectra of the 12CO and 13CO rotational ladders and HIFI spectra of selected CO line profiles would yield shock-excited gas temperatures and masses, constraining the current outflow (and thus accretion) activity in a more direct way than is possible in low excitation tracers with ground-based telescopes. HIFI observations of H2O and NH3 line profiles and abundances would provide independent present day outflow activity indicators and records of the shock history, as these species are formed above temperatures of 230 and 4000 K, respectively, and preserved in the post-shock gas. This unique Herschel data set would also address outstanding questions about the disputed origin of the Spitzer "green" emission, interstellar H2O/NH3 abundance ratios, and the role of outflow feedback in models of cluster formation.

Lead Scientist: Adwin Boogert

Allocated time: 13.5 hours

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High Velocity Cloud Properties and Origins Traced by CII Emission

The Galactic high velocity clouds are typically 10 kpc from the Sun, with many moving at high speeds through the hot (million Kelvin) gaseous halo. In addition to photoelectric heating, ram pressure can thus also heat the clouds. These heat sources are balanced by the infrared forbidden line emission of C II and O I, providing a direct window to the relevant heating processes. One particular anti-center HVC is a likely CII 158 um source, based on our study of the COBE FIRAS 158 um map and all-sky HI data. Unfortunately, the FIRAS resolution (7 degrees) is too poor to determine the location relative to the cloud and contains no useful velocity information. With the proposed Herschel PACS spectral study, we will determine whether the CII enhancement occurs at the leading side of the cloud as it falls onto the Galaxy, and the degree of ram pressure heating compared to photon heating; the C II velocities also provide crucial information. In addition, we will determine the temperature and abundance of carbon and oxygen, which will indicate if the HVC is Galactic (solar metallicity) or low-metallicity accreting material.

Lead Scientist: Alyson Ford

Allocated time: 9.4 hours

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Mapping Water and related Hydrides in Massive Protostellar outflows with HIFI

Massive outflows are known to drive a special chemical complexity due to the strong shocks they produce in the surrounding molecular material. Hydrides are key ingredients of interstellar chemistry since they are the initial products of chemical networks that lead to the formation of more complex molecules. Given their small reduced masses, their rotational lines lie at short sub-mm wavelengths, which are almost unobservable from the ground. With the HIFI instrument on board of the Herschel satellite it is now possible to observe the strongest transitions of light hydrides, in particular H2O but also the reactive ions OH+ and H2O+, which are thought to play a crucial role in the formation of OH and H2O. HIFI early results revealed that indeed water and its cation H2O+ are abundant components of the interstellar medium. The additional HIFI detection of OH+ is an important confirmation of the gas-phase route of water. Although key programs have targeted few massive sources to map the water distribution, a comprehensive study including other important hydrides such as OH+ and H2O+, and covering sources in different evolutionary phases, has not been provided yet. This project proposes a dedicated study of water and related hydrides (H2O+ and OH+) in massive protostellar outflows in order to: a) trace the water distribution throughout the different evolutionary phases of massive star formation, b) determine the contribution of water emission in the energy lost by shocks, and c) unveil the role of ions such as OH+ and H2O+ in the production of water.

Lead Scientist: Arturo Gomez-Ruiz

Allocated time: 7.5 hours

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Outflow evolution in high-mass star formation

The formation mechanism of high-mass stars and the different evolutionary phases involved in the process, still remain unclear. We recently performed single-dish HCO+ and SiO observations at millimetre wavelengths of a sample of high-mass star forming regions in search of molecular outflows. Our results indicate a decrease in the jet/outflow activity with the luminosity to mass ratio, L/M, a distance-independent parameter considered to be an estimate of time or evolutionary state. These findings are analogous to what is found in the low-mass case, which suggests that high-mass stars may form in a similar way to low-mass stars. However, uncertainties such as the unknown inclination of the outflow axes and the poor knowledge of HCO+ and SiO abundances call for more precise measurements of the outflow mass loss rates to assess the variation of this quantity with time and also associate them with the accretion rate, a crucial parameter to understand high-mass star formation.

We therefore propose to image a suitably selected sub-sample of the regions with outflows with PACS in the OI 63 micron line. According to theory, this line can be related to the outflow mass loss rate, which can thus be easily obtained. Combined with our single-dish outflow maps, and with data from the Hi-GAL survey for a better estimate of the luminosities and masses, we will calculate all the relevant parameters to assess the dependence of outflow rate on time for high-mass stars. We will also observe the OI 145 micron line to check for possible opacity effects, the CII 157 micron line to verify the presence of photo-dissociation regions which could affect the OI emission, and a number of CO transitions with both PACS and SPIRE to analyse the excitation conditions of the outflows.

Lead Scientist: Ana Lopez-Sepulcre

Allocated time: 19 hours

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Mapping the cosmic ray ionisation rate across the Northern end of the Orion A iant molecular cloud

Cosmic rays (CR) are ubiquitous in the Galaxy and have the important role of ionizing the dens gas of the ISM. New Herschel observations have shown the huge diagnostic power of the OH+ fundamental transition to measure the CR ionization rate in diffuse clouds. Based on previous "serendipity" observations toward OMC2-FIR4 within the KP CHESS, we discovered a tenuous foreground cloud absorbing the fundamental OH+ line. Similarly, Gupta et al. (2010) found an OH+ absorption component at a similar velocity towards Orion KL and estimated a large CR ionization rate more than 10 times larger than the average value observed in diffuse clouds . We propose here to roughly map the CR ionization rate in the direction of the OMC2 and OMC3 complex to understand its extent, nature, and, finally, the source of ionization.

Lead Scientist: Ana Lopez-Sepulcre

Allocated time: 5.2 hours

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SABER: Spectral Analysis of the Bowshock Emission in a Runaway

Bowshocks around runaway OB stars are some of the most spectacular objects in the mid/far infrared, covering in some cases as much as half a degree across the sky. The bowshocks are essentially enormous gas shells contained by ram pressure where the dust trapped in their interiors reprocesses the UV flux from the parent OB stars and re-radiates it in the infrared. The pressure balance between the stellar wind and the ISM, also implies a tight relationship between their physical properties, and therefore, bowshocks from runaway stars provide a powerful tool to probe the interstellar medium and/or the properties of the OB stellar wind. The formation of these shells requires very efficient cooling that is expected to take place through the emission of a wealth of atomic fine structure lines, like [OI] 63.2 or [NII] 205.2 micron. Because the diffuse nature of these shells it has been very difficult to confirm this expectation using spectroscopic observations. In this project we propose to use the PACS spectrometer to observe the zeta Oph bowshock in order to better understand and constrain the physical conditions of its gas shell, its dust properties, its turbulence, and in such a way that will allow to use zeta Oph as a template to make sense of the physical properties of the many more runaway bowshocks are continuously being discovered.

Lead Scientist: Alberto Noriega-Crespo

Allocated time: 6.2 hours

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Turbulent dissipation in the diffuse medium : its dynamics revealed by combined HIFI observations of 13CH+ and SH+

Among all species detected in the diffuse interstellar medium, CH+ and SH+ are unique. Since their main production pathways are highly endo-energetic, their large observed abundances are likely the signature of the dissipation of turbulence. In addition, since the energies involved in their formation differ by more than a factor of 2, a comparative analysis of CH+ and SH+ provides essential clues on the nature of the dynamical processes involved in turbulent dissipation.

We propose here to perform sensitive Herschel/HIFI observations of 13CH+ and SH+ in absorption towards 5 background dust continuum sources located in the inner Galaxy : W49N, G34, W51, DR21(OH), and W33A. Each line-of-sight samples kiloparsecs of diffuse interstellar matter. Given the sensitivity and resolution of HIFI, we propose to reach a signal/noise ratio of about 300 in order to analyze the velocity structure of individual clouds along the sightlines. This project has two main goals : (1) characterize the kinematic signatures of the 13CH+ and SH+ absorption lines and compare them, statistically, to those of molecular species whose formation routes are less (or not) endothermic and (2) confront the 13CH+ and SH+ abundances to model predictions in order to directly derive for the first time the turbulent dissipation rate and the ion-neutral velocity drift driving dissipation in individual diffuse clouds.

Lead Scientist: Benjamin Godard

Allocated time: 14.7 hours

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Searching for the onset of energetic particle irradiation in Class 0 protostars

Several evidences tell us that the first stages of low mass star formation are very violent, characterized by, among other phenomena, an intense irradiation of energetic (MeV) particles. The goal of this proposal is to search for signs of MeV particle irradiation in a sample of low to intermediate mass Class 0 protostars. At this end, we propose to observe a selected list of high J HCO+ and N2H+ lines in a selected sample of sources. Based on the observations obtained within the KP CHESS, we estimate a total observing time of 20.5 hours.

Lead Scientist: Cecilia Ceccarelli

Allocated time: 19.6 hours

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Peering into the engine of a jet-driven bowshock : TMC1B1

Jet-driven bowshocks seem to be rather ubiquitous in star-forming regions. If the large-scale bow is commonly observed and its kinematics, the actual engine of the outflow, the Mach disk region where the gas is accelerated, has never been detected until now.

Recently, we have found observational evidence of the long-searched engine of outflows in the giant molecular bowshock TMC1B1 together with the driving jet, in Taurus (d=140 pc).

which allows Herschel to resolve the cooling region of the shock. We propose to use Herschel to investigate the dynamics and physical structure of TMC1B1, a potential benchmark for jet-driven bowshocks studies.

Lead Scientist: Cecilia Ceccarelli

Allocated time: 5 hours

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Where is chlorine in shocked regions?

As part of the GT Herschel Program CHESS we detected for the first time hydrogen chlorine in a protostellar shock, L1157-B1 (Codella et al. 2011). One of the most surprising results of this work was the lack of enhancement in the abundance of HCl with respect to dense interstellar clouds, implying that HCl is not enhanced by the passage of a shock. This means that either chlorine is not sputtered during the passage of the shock (unlikely as Si is sputtered) or that HCl is not the main reservoir of clorine in shocked regions (unlike in dense interstellar clouds). In this proposal we propose to observe HCl in a sample of shocked regions in order to determine whether this result is unique to L1157-B1. We stress that given the weakness of the HCl emission in shocks and the strong atmospheric water absorption at the requested frequency (626 GHz), the present experiment cannot be reasonably performed from ground, making of Herschel OT2 the last chance to reach the present goals.

Lead Scientist: Claudio Codella

Allocated time: 7.2 hours

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Observations of a Sleeping Giant: A Herschel Survey of the California Molecular Cloud

We propose to use the Herschel telescope in the unique SPIRE/PACS parallel mode configuration to completely map the California Molecular Cloud in five photometric bands to the confusion limit at SPIRE submillimeter wavelengths. At a distance of 450 pc the California cloud rivals the famous Orion A cloud as the largest and most massive GMC in the solar neighborhood. However the California Molecular Cloud contains more than an order of magnitude fewer YSOs than Orion and is characterized by a star formation rate that is an order of magnitude lower than that in Orion. It is thus an ideal laboratory for studying the physical conditions that give rise to low rates of star formation in GMCs and thus for ultimately determining the physical factors that control the star formation rate in molecular gas, critical information required for understanding galaxy formation as well as star formation. The specific goals of this experiment are to: 1) identify and characterize the dense core population, 2) construct the core mass function (CMF) of the cloud, 3) obtain a more complete and accurate census of the YSO population and thus star formation rate in the cloud, and 4) accurately determine the nature and evolutionary status of the individual YSOs in the cloud via modeling of their SEDs. For this purpose the Herschel data will be combined with ancillary ground-based and space-based (Spitzer) photometric measurements following a method we successfully tested in a previous investigation of the natures of the NGC 2264 and IC 348 YSO populations. The proposed Herschel observations will be part of a coordinated, multi-wavelength campaign modelled on our highly successful study of the Pipe Nebula and will provide results that will constitute an important complement to those Herschel programs studying molecular clouds with rich star formation activity. So far, only about half of the California cloud is covered by planned Herschel observations, and we thus propose to complement and double the coverage of existing programs.

Lead Scientist: Charles Lada

Allocated time: 25.2 hours

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Intermediate Mass YSOs: getting to the core of the matter

Due to a dramatic increase in gas-phase abundance above temperatures of 100 K, water emission illuminates the important 'milestones' of star formation. Gravitational collapse, accretion shocks, protostellar heating of envelopes and disks, and the injection and motion of outflows into the protostellar envelope all glow in water. At the same time, water in absorption probes the conditions of the cold gas. Determination of water abundance throughout the envelope allows us to place strong constraints on the the physical structure of the envelope and energy transfer occurring within it.

Analysis of H2O and H2018O transitions observed with HIFI towards intermediate mass Young Stellar Objects have shown that, contrary to expectations, the ground state H2-18O line (547.676 GHz) does not trace the warm inner envelope. Test observations towards two of our sources have confirmed model predictions that the higher excitation line at 1095.627 GHz can be used to probe the warm inner envelope and hot core.

Following this result, we propose to observe the remaining intermediate mass YSOs on our source list. We request 12.3 hours to perform HIFI DBS observations in band 4b in order that we may determine the water abundance in the inner regions of these proto-stellar envelopes.

Lead Scientist: Carolyn McCoey

Allocated time: 6.3 hours

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Evolution of water emission in intermediate mass YSOs

Intermediate mass YSOs are studied as part of the WISH KP. We find our source sample is too limited to identify properties associated with stellar evolution. With this proposal we ask for time to observe two more intermediate mass YSOs with HIFI and PACS.

When looking at line profiles among or source set a confused picture appears. NGC 7129 FIRS 2 and LDN 1641 are both Class 0 YSOs but have very different line profiles. Similarly, the Vela sources are both Class I sources and even have almost the same bolometric luminosity but display very different spectra. It is noteworthy that line profiles of the Class 0 NGC 7129 FIRS 2 are very similar to the line profiles of the Class I Vela IRS 17. Furthermore, the most evolved source, AFGL 490, is most similar, albeit brighter, to one of the least evolved sources, LDN 1641.

We require more observations in order to assess if there is any relation in line profile with evolutionary state. We ask for time to observe the Class 0 intermediate YSO, Cep E-mm, and the Class I/II sources, LkHa 224.

Lead Scientist: Carolyn McCoey

Allocated time: 11.3 hours

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Exploring the role of CII in current Spinning Dust Models

We propose HIFI observations of the CII fine structure line at 158 micron (1.9THz) in 22 pointings distributed across four Galactic anomalous emission regions (the Perseus cloud, LDN 1780, LDN 675 and LDN 1111). The currently favoured explanation for the observed anomalous microwave emission is that of electric dipole radiation from rapidly rotating small dust grains (PAHs and/or VSGs), commonly referred to as spinning dust. Although this hypothesis predicts that the source of the excess emission is due to dust, the small dust grains are sensitive to the ionisation state of the gas, and hence the spinning dust models have a dependancy on the abundance of the major gas ions. CII observations will enable us to investigate this dependancy, and combining these observations with the available mid- to far-IR observations will permit a complete analysis of the role of both the dust and gas in regions of anomalous emission. We request a total of 14.9 hrs of HIFI observing time.

Lead Scientist: Christopher Tibbs

Allocated time: 14.9 hours

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Ammonia as a Tracer of the Earliest Stages of Star Formation

Stars form in molecular cloud cores, cold and dense regions enshrouded by dust. The initiation of this process is among the least understood steps of star formation. High!resolution heterodyne spectroscopy provides invaluable information about the physical conditions (density, temperature), kinematics (infall, outflows), and chemistry of these regions. Classical molecular tracers, such CO, CS, and many other abundant gas!phase species, have been shown to freeze out onto dust grain mantles in pre!stellar cores. However, N!bearing species, in particular ammonia, are much less affected by depletion and are observed to stay in the gas phase at densities in excess of 1e6 cm!3. The molecular freeze!out has important consequences for the chemistry of dense gas. In particular, the depletion of abundant gas!phase species with heavy atoms drives up abundances of deuterated H3+ isotopologues, which in turn results in spectacular deuteration levels of molecules that do remain in the gas phase. Consequently, lines of deuterated N!bearing species, in particular the fundamental lines of ammonia isotopologues, having very high critical densities, are optimum tracers of innermost regions of dense cores. We propose to study the morphology, density structure and kinematics of cold and dense cloud cores, by mapping the spatial distribution of ammonia isotopologues in isolated dense pre!stellar cores using Herschel/HIFI. These observations provide optimum probes of the onset of star formation, as well as the physical processes that control gas!grain interaction, freeze!out, mantle ejection and deuteration. The sensitive, high!resolution spectra acquired within this program will be analyzed using sophisticated radiative transfer models and compared with outputs of state!of!the!art 3D MHD simulations and chemical models developed by the members of our team.

Lead Scientist: Dariusz Lis

Allocated time: 16.7 hours

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High frequency water masers with Herschel/HIFI

Using HIFI, we will observe three rotational transitions of water vapor, all predicted to be strong submillimeter masers, toward the massive star-forming regions W49N and W51 (Main); and toward the oxygen-rich evolved stars VY CMa and U Her. The target transitions are the 5(23) - 4(41), 5(24) - 3(31), and 6(34) - 5(41) pure rotational lines of water at 621, 970, and 1158 GHz. In combination with maser transitions of lower frequency that can be observed from the ground, the proposed observations will constrain the conditions of gas temperature, gas density, and IR radiation field within the maser-emitting region, providing important constraints upon the maser pumping mechanism. In the case of the star-forming interstellar regions, the proposed observations will also constrain the nature of the shock waves that power the maser emission.

Lead Scientist: David Neufeld

Allocated time: 10 hours

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Unveiling the spectral shape of warm Galactic dust emission

The largest dust grains dominate the total dust mass, as well as the observed emission in the far-infrared (FIR) domain. They contribute to the efficient cooling in the FIR and submillimeter/millimeter (submm/mm) wavelengths, essential for the condensation of the ISM and the star formation process. Understanding the variations in dust emissivity is of primary importance, because they directly affect the accuracy of any mass determination using the Herschel photometric data. They are also extremely interesting in the prospect of understanding dust physics. For long time, the lack of data in the submm domain has induced to model the submm dust emission by a modified black-body, characterized by the mean dust temperature and a temperature and wavelength independent spectral index. However, analyses of recent data have shown a significant flattening of the dust emission spectrum in the submm/mm domain, for temperatures around 20 K. Emissivity variations also seem to be temperature-dependent. Two main models of the FIR/submm emission have been proposed to explain astrophysical observations, leading to different estimates of the interstellar medium characteristics. The present proposal aims at obtaining Herschel low resolution spectroscopic data towards the warmest regions of the ISM, in order to measure precisely their dust continuum emission. Indeed, dust processes occuring in warm/hot environments are poorly known. This unique combination of PACS and SPIRE spectroscopy for a sample of 7 compact/ultra-compact HII regions, accounting for 15.4h observing time, will allow us to efficently discrimate between possible dust models.

Lead Scientist: Deborah Paradis

Allocated time: 15.4 hours

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Unveiling the water puzzle in cold PDRs: The Horsehead case

While Herschel observations of water vapour in warm regions (T_gas >> 100 K) driven by energetic processes (outfows, shocks, hot cores, etc.) have confirmed large abundances of water vapour (~10^-5), the inferred gas phase H2O abundance in dark clouds is very low, ~10^-10. A detailed balance between freeze-out, ice-mantle desorption and gas-phase chemistry is required to explain this orders-of-magnitude abundance difference.

The Horsehead nebula is particularly well-suited to investigate grain surface chemistry in a UV irradiated environment. Its relatively low UV illumination (~60 in Draine units) implies low dust grain temperatures, from T_dust=30K in the PDR to T_dust=20K deeper inside the cloud. Therefore, the release of the grain mantle products into the gas phase, water vapour in particular, is dominated by UV-induced photo-desorption and not by thermal evaporation (as in other warm PDRs such as the Orion Bar). Besides, owing to its simple edge-on geometry, the Horsehead is very close to the prototypical kind of source needed to serve as model benchmark.

A relatively low water vapour beam-averaged abundances (~5x10^-9) was derived from a single position of the o-H2O ground-state line towards the so-called "IR peak" of the Horsehead PDR. However a detailed comparison with sophisticated PDR models including gas and grain chemistry is not possible due to our complete ignorance about the true H2O spatial distribution as one moves from the UV-illuminated cloud surface to the inner shielded cloud. We propose here to map with HIFI the o-H2O 557 GHz line on a cut across the PDR front, and extract the spatial information required to constrain the role of water freeze-out and water ice photodesorption as a function of cloud depth.

Lead Scientist: David Teyssier

Allocated time: 4.6 hours

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HIFI and SPIRE spectroscopy of HOPS 87: a bright water-rich protostar without an outflow

We propose to use Herschel HIFI and SPIRE to observe emission lines of water and CO in a low-mass Class 0 protostar, HOPS 87 (a.k.a. OMC-3 MMS 6N), for which we have characterized the water emission spectrum extensively with Spitzer-IRS and Herschel-PACS. HOPS 87 is the most luminous source of water emission lines found in a survey of low-mass YSOs, but has very little other emission that could be taken as evidence of a high-velocity outflow; if it truly lacks such an outflow at present it provides a rare opportunity to examine emission from the infalling envelope and potentially the envelope-disk accretion shock. With HIFI spectra we will determine whether or not the water emission arises in a high-velocity outflow, and detect separately the kinematic signatures of the warm inner envelope, the outflow-cavity walls, and perhaps the envelope-disk accretion flow. Confirmation of the detection of dense water in the disk accretion flow, which has been suggested as the origin of the mid-infrared (20-40~\micron ) water emission, would be the first unambiguous detection of this flow and is a major goal of this proposal. With SPIRE spectra we will complete our Spitzer-IRS and Herschel-PACS census of water and CO emission in this object, thereby obtaining a particularly complete and detailed account of physical conditions in the HOPS 87 envelope.

Lead Scientist: Dan Watson

Allocated time: 12.6 hours

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H3O+ as a tracer of Galactic Center Black Hole activity

The center of the Milky Way harbors a now dormant massive black hole (Sgr A*). Over the years evidence has mounted that Sgr A* released an energetic X-ray flare nearly 100 years ago. The strongest evidence for this is the detection of reflected X-ray emission towards molecular clouds in the central regions of the galaxy. We believe that we have directed direct evidence of the effects of this flare due to the presence of warm (excitation termperature ~ 600-800 K) H3O+ in the envelope of the Sgr B2 molecular cloud. These observations were obtained as part of the HEXOS key program and in all we have detected H3O+ J,K = 1,1 through 11,11 each in absorption. These are the inversion transitions that lie at the bottom of a given K ladder. For J,K > 3 the transitions cannot be be excited by conventional collisional excitation or by radiative pumping. Instead our model strongly favors that the rotationally warm H3O+ is the result of formation pumping due to the strong impinging X-ray flux, potentially from Sgr A*. We propose to follow up this fantastic result with a small search for rotationally warm H3O+ absorption towards other galactic center molecular clouds that are strong continuum sources and are in close proximity to Sgr A*. This proposal follows a very interesting molecular astrophysical puzzle that may be a direct link to activity from the central engine of our galaxy.

Lead Scientist: Edwin Bergin

Allocated time: 16 hours

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The Herschel/HIFI insight on the CH+ puzzle in the diffuse medium

Seventy years after its discovery in the diffuse interstellar medium, the origin of the CH+ cation is still elusive. Herschel/HIFI offers a unique opportunity to disclose the underlying gas dynamics at the origin of CH+ in the diffuse medium by allowing high sensitivity and high spectral resolution observations of the CH+(J=1-0) transition, unreachable from the ground: it is the only instrument, for the decades to come, able to bring a completely new look at this resilient puzzle.

The abundant CH+ ion is not only a sensitive tracer of the most tenuous phases of the interstellar medium but it appears as a specific tracer of turbulent dissipation, because its formation route is highly endoenergic. We propose absorption spectroscopy observations of the CH+ J=1-0 line, against 7 background dust continuum sources, bright enough to allow the sample Galactic environments with highly different turbulent dissipation rates. We take advantage of the high opacity of the CH+(1-0) transition to search for CH+ in more diffuse components than previously observed: in the high-latitude diffuse medium, in gas out of the Galactic disk and in the outer Galaxy. The unknown H2 molecular fraction of these poorly explored parts of the diffuse Galactic component will be inferred from the CH absorption lines.

The primarily goal of this project is the comparison of the CH+ abundances with model predictions, in which turbulent dissipation proceeds either in low-velocity shocks or intense velocity-shears. Another goal is testing the possibility that CH+ forms at the turbulent interface between the two thermally stable phases of the interstellar medium. Last, as HF, CH+ is a potential sensitive tracer of diffuse molecular matter in the early universe. Understanding its origin and the dissipative processes that it traces will shed a new light on galaxy formation and evolution.

Lead Scientist: Edith Falgarone

Allocated time: 11.3 hours

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Unveiling the origin and excitation mechanisms of the warm CO OH and CH+

Photon Dominated Regions (PDRs), where physics and chemistry are driven by FUV photons, show an extreme rich warm gas photochemistry closely related to proto-planetary disks and starburst galaxies. Spatially resolved studies of nearby PDRs are essential as they enable us to characterise the physico-chemical processes that control the regions and can serve as templates for compact systems where these process cannot be disentangled. The rotationally excited lines of CO, OH and CH+ probe the warmest PDR gas layers, providing strong constrains for the modelling of both the complex physics and chemistry driven in the presence of FUV fields. The emission of these lines have been recently connected to the presence of high-density structures (clumps or filaments). We propose to map the high-J CO, OH and CH+ lines in the Orion Bar, using fully sampled PACS maps and HIFI observations. These observations will probe the spatial thickness of the line emission layers necessary for detailed comparison with the state of the art PDR models. This will enable us to characterize the origin and excitation mechanism of these high rotational lines improving our understanding of the physics and chemistry of the warm phase in the ISM.

Lead Scientist: Emilie Habart

Allocated time: 12.7 hours

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Characterisation of the Extended Gas Components in Protostars with Herschel

This proposal aims at investigating the early protostellar evolutionary phases of protostars. In addition to the study of their fundamental properties (e.g. density, temperature, infall rate, accretion rate), a major focus of this proposal is the interpretation of the more extended gas components connected to the protostar. Extended envelopes, outflow shocks and jets and PDRs originating in the outflow cavities can potentially ontribute to this complex more extended emission. The spatial discrimination between these different excitation mechamisms and the quiescent underlying gas requires the combination of spatial and spectral information on several diagnostics that span a range of physical and chemical conditions. We propose PACS full SED oversampled spectral mapping around a carefully selected sample of 7 protostars at different evolutionary stages in the Chamaeleon-Musca cloud complex. This region is particularly suited to spatially resolved studies due to its proximity. This proposal is one of the many spin-off projects with an origin in the Gould Belt Key Programme and will complement other Herschel studies of protostars.

Lead Scientist: Elena Puga

Allocated time: 23.4 hours

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Water In Low-mass protostars: the William Herschel line Legacy (WILL)

We propose a survey of water lines toward an unbiased flux limited sample of low-mass protostars newly discovered in recent Spitzer and Herschel Gould Belt imaging surveys. Water has long been speculated to be a key molecule in the chemistry and physics of star-forming regions, but its actual role is only now starting to emerge thanks to Herschel. Initial HIFI data reveal surprisingly complex water emission profiles, which uniquely trace the different dynamical processes during the embedded phase of star formation (outflows, jets, shocks, infall, expansion). By using lines originating from different energy levels, the water abundance in the cold and warm gas can be determined as function of velocity and thus the chemical processes that shape them (gas-grain interactions, high temperature reactions). The ortho/para and HDO/H2O ratios hold important clues on the temperature history of the clouds and on the journey of water from cores to disks and planets. Combination with PACS data on water and related species (O, OH, CO) can determine the total gas cooling budget and can quantify the 'feedback' of the protostar on its surroundings in terms of UV radiation and shocks.

The unbiased WILL sample allows all of these questions to be studied as function of source characteristics and protostellar evolution in a statistically significant way, thus charting the processes that shape the emerging young star and disk in the critical period from the collapse phase to the envelope dispersion stage. No other space-based heterodyne mission will be available to provide velocity resolved water lines for at least 30 years, making this program a true Herschel Gould Belt line emission legacy.

Lead Scientist: Ewine van Dishoeck

Allocated time: 133.6 hours

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Depletion Cores - the O2 Hideout?

Molecular oxygen has proven to be the most elusive molecule in the interstellar medium. Despite the fact that it in theory forms easily in both warm and cold dense gas, extensive searches with SWAS, Odin and Herschel have only resulted in detections in two sources. In addition, upper limits in various astronomical environments are at levels of 1000 times less abundant than predicted by chemical models.

This situation requires either for atomic carbon to be abundant enough to suppress the O2 by CO formation, or for atomic oxygen to accrete onto grains and remain bound there. However, the binding energies of atoms to grains are highly uncertain and high abundances of OI in depleted gas have both been directly observed and inferred from observations of other molecules. A possible explanation is that OI is bound to grains by fixing (get hydrogenated to form ices) rather than sticking (van der Waals bonding to the surface potential), which will become less efficient in high density gas.

Based on this, our calculations show that molecular oxygen could be abundant in dense cores of high CO depletion. To test this theory, we propose to search a small sample of starless depletion cores for emission in the low excitation O2 line at 487.249~GHz using Herschel HIFI.

Lead Scientist: Eva Wirstroem

Allocated time: 3 hours

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Determining the Ice Desorption Mechanism in Cold Molecular Clouds

Interstellar ices are readily formed from accretion of atoms and molecules onto cold dust grains, and in dense cores the gas would be depleted in all heavy molecules were it not for the operation of some non-thermal desorption process.

Methanol molecules are only formed efficiently from hydrogenation of CO molecules accreted onto grains, but is still widely observed in cold dense clouds. This attests to the operation of desorption processes not related to the heating up of the gas from a nearby star. Proposed mechanisms for injecting the ice mantle molecules into the gas-phase includes both continuous processes, such as cosmic-ray impacts, photodesorption, or ejection upon formation, and more transient ones such as clump-clump collisions, and effects of embedded protostars influencing the chemistry through shocks or dissipation of magnetohydrodynamic (MHD) waves. The presence of distinct peaks of methanol emission at positions significantly offset from protostars, however, implies that the desorption process is indeed transient, and likely to also disrupt a major part of the ice mantles. This would lead to very high water abundances at these peaks, clearly distinguishable from what is expected from photodesorption or steady-state gas-phase chemistry.

In order to constrain the active ice desorption mechanisms in cold molecular clouds, we thus propose to use HIFI to observe the ground state transition of ortho water at three different methanol peaks: two at different distances from the Class I protostar Barnard 5 IRS1, and one in L1512, a region free from protostellar activity.

Lead Scientist: Eva Wirstroem

Allocated time: 1.6 hours

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Spatial distribution of HF emission in photon-dominated regions

The HF molecule is an excellent tracer of H2, even at low column densities where CO is photodissociated, as shown by widespread absorption in the 1--0 line at 1232 GHz seen with Herschel. We have made the surprising observation that this line appears in emission towards the Orion Bar, which is where ultraviolet radiation from the Trapezium stars hits the molecular cloud and causes heating and dissociation. Three mechanisms may cause this unusual effect: thermal excitation, which requires very high gas densities; radiative pumping by dust continuum or H2 line emission at ~2.5 microns; or chemical pumping where most HF is formed in the J=1 state. These models each predict a distinct spatial distribution of HF, which is why we hereby propose one-dimensional maps of HF in the Orion Bar and two similar regions. Combined with existing maps of CO and dust emission, the new data will constrain the density structure of molecular clouds in the low column density regime which is inaccessible to other telescopes, and thus offer fundamental insight into the physics of the interstellar medium.

Lead Scientist: Floris van der Tak

Allocated time: 1.5 hours

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A Water survey of massive star forming clumps in the inner Galaxy

Water, as a dominant form of oxygen, the most abundant element in the universe after H and He, controls the chemistry of many other species. It is a unique diagnostic of warm gas and energetic processes taking place during star formation.

We therefore propose to exploit the unique opportunity of Herschel to study water in large, statistically significant, flux limited samples of massive star forming regions detected in the recently completed ATLASGAL submm dust continuum survey of the inner Galactic plane.

In the last years, our view of massive star forming regions has dramatically changed by Galactic plane surveys covering cm to IR wavelengths. These surveys enable us for the first time to study ALL evolutionary stages of massive star formation (MSF) in an unbiased way. Water, acting as a natural filter for warm, dense gas, allows to probe the chemical and physical conditions in all of these stages close to where the massive stars are forming or just have been formed.

ATLASGAL observed submm dust continuum emission as best tracer of the earliest phases of MSF since it is directly probing the material from which the stars form. As a large unbiased survey it provide the statistical base to study the scarce and short-living protoclusters as the origin of the massive stars and the richest clusters in the Galaxy and supplies us with a legacy value sample of MSF regions for the water follow ups.

Water is typically seen with strongly increased abundances in broad line wings, providing a new, sensitive probe of shocked outflowing gas. In addition, the envelope is probed in a combination of absorption and emission with a clear jump in abundance in the warm inner regions close to the forming massive stars. Only Herschel can provide a water survey of a large sample of ATLASGAL selected sources to study water through the evolution of massive star forming regions with a statistically significant sample size.

Lead Scientist: Friedrich Wyrowski

Allocated time: 30.6 hours

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A novel search for episodic accretion onto the youngest protostars

We propose to use second epoch PACS+SPIRE photometry of nearby star-forming regions to detect episodic accretion events onto the youngest, Class 0, protostars. It is well accepted that the bolometric luminosities of these young protostars fall at least an order of magnitude below the steady-state accretion luminosities needed for their assemblage and that as much as 90% of the total mass must be accreted during episodic events. Optical and IR monitoring of older, non-shrouded pre-main sequence stars has revealed powerful episodic events (FUors and EXors) but not until Herschel have we been able to map large enough star-forming regions to the depths necessary to perform this time-domain survey for episodic accretion onto Class 0 protostars.

The proposed 21.8 hour survey of Aquila, NGC 1333, Oph L1688, and IC 5146 will map more than 200 known Class 0 protostars, 500 Class I protostars, and thousands of pre-stellar cores. These second epoch multi-wavelength observations allow us to be sensitive to order unity variations in bolometric luminosity (and temperature) and thus while we are unlikely to observe any rare, extreme accretion events, we will be able to place constraints on the importance of more common accretion enhancements in supplying mass to the protostar. All interesting detections will become prime candidates for follow-up detection from the ground.

Our proposed Herschel program is our best chance to probe accretion variability for the youngest protostars, which are in an evolutionary stage that has not been observable in previous or ongoing variability surveys.

Lead Scientist: Greg Herczeg

Allocated time: 19 hours

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Testing the Water Predictions of Thermo-Chemical Models of Externally-Illuminated Molecular Gas

Models that include the key radiative and chemical processes necessary to understand the emission from externally-illuminated molecular gas - so called thermo-chemical or PDR models - are now commonly invoked to account for the line flux from far-ultraviolet illuminated galactic and extragalactic molecular clouds as well as protoplanetary disk surfaces irradiated by their central stars. Whether these models are correct in general, and for water in particular, remains an open question; using present observations to test these models has proven difficult because of the complexity of the regions observed and the resulting uncertainty in many of the model input parameters. Using HIFI, we will obtain scan maps in the ground-state 1(10)-1(01) ortho-water transition at 557 GHz across the ionization front/molecular cloud interface toward two well-studied, uncomplicated regions with favorable geometry - Cepheus B and the starless dark globule DC 267.4-7.5. The proposed observations will produce measures of the gas-phase water abundance across these two atomic-to-molecular transition zones, which will be compared to the model-predicted profiles of water emission versus Av into the clouds. Because of the edge-on geometry and the absence of known embedded sources along the scan paths, the proposed observations provide the best, most controlled test of these models to date. Both regions have been successfully observed previously with SWAS, but SWAS's much larger beam size made the kind of study proposed here impossible. Neither the Herschel WISH nor PRISMAS Key Programs contains observations that come close to offering as rigorous a test of the models as constructed here. Because these observations require a space-borne telescope with both high spatial and spectral resolution, they cannot be carried out from any other observatory in the foreseeable future.

Lead Scientist: G.J. Melnick

Allocated time: 8.8 hours

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Solving the puzzle of water excitation in shocks

Water is a highly complementary diagnostic to the commonly used CO molecule. It has a central role in protostellar environments and in outflow shocks, being one of the main coolants and the most sensitive to local conditions. As part of the WISH key program, a survey of several H2O lines at different excitation has been performed with HIFI at two selected shock spots in the bright L1448 and L1157 outflows. These observations and their analysis have given unexpected results, that contrast with current models of water emission in shocks. However, the validity of these results needs to be checked with suited high S/N observations, allowing to remove some of the free-parameters of the line excitation modeling and to derive water abundance.

The goal of this proposal is to clarify the controversial issues raised by these previous observations by mapping with HIFI a 40 arcsec area covering two shock positions along the NGC1333-IRAS4A outflow, identified as very bright in H2O from our PACS map at 1670 GHz, in key spectral transitions of H2O and CO. These observations will provide unprecedented constraints on the physical and chemical properties of the gas associated with the water emission, as a function of velocity, and on the properties of the shock at the origin of the emission. In particular, mapping the H2O lines will allow us to remove the uncertainty originated by the largely different beams of the observed transitions. The CO(16-15) will be also observed: this line comes from the same high excitation gas as that traced by H2O and thus will provide a tool to derive an H2O/CO abundance ratio much more reliable than what is obtained with the low-J CO transitions observed from ground.

We point out that it is crucial to solve the issue of water excitation in shocks before the end of the Herschel mission, in order to correctly interpret all the data acquired on H2O in outflows by Herschel and provide reliable constraints on water abundances and shock dynamics.

Lead Scientist: Gina Santangelo

Allocated time: 19.6 hours

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Star Formation Within the Giant HII Region W80:

We propose to obtain a contiguous 5.3 square degree square map of the extended HII region W80 using PACS and SPIRE. Contained in this field of view are the little studied North American and Pelican nebulae, and a dark molecular cloud region referred to as the Gulf of Mexico. This region has not been globally mapped by Herschel. The distance to W80 (and regions therein) is about 600 pc making it the next nearest region similar to Orion. 2MASS extinction mapping reveals Av>5 mag over most of W80, and cores in several areas exceed 30 mag. Spitzer IRAC and MIPS have observed this entire complex, yielding catalogues of hundreds of potential YSOs. We have conducted a wide-field H2 2.12 micron partial survey for shocks and outflows and have discovered dozens of highly embedded energetic protostellar outflows and jets distributed over the cloud complexes. The region rivals NGC 1333 known to harbor the highest concentration outflow sources. The O-stars that produce the ionizing UV radiation and these new young, accreting sources are responsible for the intra-cloud dispersal and the triggering of star formation in surrounding regions. Herschel photometry at 5 bands (70, 160, 250, 350, and 500 microns) are required to complete the measurement of the SEDs thereby allowing classification, measure the temperature and masses of the disks, and to better define the extended structure and morphology of the intra-cloud medium, including IRDCs, pillars, and filaments. Herschel is vastly superior to mapping large scale structure of the cold dust, warm edges, and hot dust associated with PDRs, compared with mm-surveys (eg., ATLASGAL and BGPS) as these latter surveys tend to spatially filter out large scale structure >7' in their data processing. Herschel will provide the essential high angular resolution and sensitivity data needed to quantify each SED and to map the morphology of the complexes.

Lead Scientist: Guy Stringfellow

Allocated time: 6.8 hours

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Formation signatures and carbon budget of molecular clouds

The interstellar medium (ISM) is mainly comprised of ionized, neutral atomic and molecular gas. One of the most important constituents of these phases is carbon in its ionized/neutral/molecular form (C^+, C^0 and CO). However, a coherent analysis of the different phases at adequate resolution (Jeans length ~0.2pc) is lacking. We therefore want to re-evaluate the ISM carbon budget via observing primarily C^+ at 1.9THz, C^0 (at 492GHz), and CO(2-1) with Herschel, APEX and the IRAM 30m at high spatial resolution (11''-13'') for several infrared dark clouds (IRDCs). This proposal is a follow-up of a guaranteed time pilot study for the line of ionized carbon [CII] toward one IRDC. In this open time project we like to extend the sample to a total of five IRDCs in different environments. With the combined data of the different carbon phases we can address: (a) How do the relative abundances change with evolutionary stage? (b) Are the different phases mainly excited by internal or external radiation sources? (c) How important are the phase changes for the carbon cooling budget of the ISM? (d) Can we identify cloud formation signatures (e.g., turbulent flows)?

Lead Scientist: Henrik Beuther

Allocated time: 19.3 hours

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A Deep Search for the Molecular Anions CN- CCH- OH- and SH- in the Galaxy

We propose a sensitive search towards six Galactic sources for the small negative molecular ions (anions) --- CN-, CCH-, OH-, and SH- --- with Herschel's Heterodyne Instrument for the Far-Infrared (HIFI). The full significance of anions in astrophysics is far from understood, and molecular anions may have a much broader impact on the chemistry and physics of astronomical sources than is currently appreciated. In dark clouds and low-mass star-forming regions, reactions of molecular anions are thought to enhance the abundances of neutral polyynes and cyanopolyynes. In circumstellar shells of evolved carbon stars, anions are theorized to form by proton transfer reactions of neutral carbon chain radicals with H-, as well as through reactions of atomic N with large carbon chain anions. By influencing the ambipolar diffusion rate, anions may regulate the dynamics of star formation in magnetized plasmas around collapsing molecular cloud cores. Because the abundances of anions are sensitive to electron attachment and photodetachment rates, anions can serve as direct probes of electron densities and cosmic-ray ionization and photoionization rates within interstellar clouds, provided the formation and destruction processes of anions are known. The main question we seek to address is just how widespread anions are in the Galaxy. The four anions we propose to study are structurally simple molecules, with precursors that are abundant in the interstellar gas. The observations here will provide key information on the distribution small molecular anions, which, when combined with chemical models of the observed anion abundances and their dependence on conditions within their astrophysical environments, will advance our understanding of the role of anions in the physics and chemistry ofastronomical sources.

Lead Scientist: Harshal Gupta

Allocated time: 13 hours

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Far-infrared spectroscopic imaging study of interstellar material around eta Carinae

Our science goal is to study the influence of massive star-forming activities to the physical and chemical conditions of interstellar space. Our target region in the Carinae Nebula especially region around Eta Carinae, where massive star clusters and molecular cloud complexes are observed and there are indication of past activities of stellar wind and current activities of star formation is observed. We use far-infrared atomic fine structure lines as a tool to study the influence of massive star to the interstellar material surrounding it. Observing area is selected from wide area spectroscopic imaging of AKARI observations. Herschel Space Observatory will show the high angular resolution images of the selected regions with high activities. Eta Carina and their surroundings are at relatively low extinction region, and comparative study in X-ray, optical, infrared and radio observations can be done easily. Detailed observation of massive star forming region in Carina Nebula is important to understand the role of massive star-forming region in general in our galaxies and external galaxies including high extinction regions.

Lead Scientist: Hiroshi Matsuo

Allocated time: 7.8 hours

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HIFI Observations of Cold Cores in Infrared Dark Clouds

Infrared Dark Clouds (IRDCs) are thought to host the earliest stages of high-mass star formation, an epoch that is still poorly understood. Gound-based millimeter observations have found that many IRDCs have embedded cores, and Herschel PACS and SPIRE photometry has made it possible to image many of these very cold cores via their dust emission. We have used the Submillimeter Array (230GHz) to observed a sample of cold IRDCs that are dark even at PACS70, but which contain bright cores seen in emission in the SPIRE bands. The SMA spectral maps and the molecular chemistry suggest at least three early stages of star formation that we have tentatively modeled as reflecting three progressive temperature and evolutionary stages. Unfortunately in the youngest, coldest sources most diagnostic molecules are either frozen out onto grains or have not yet assembled. Nitrogen hydrides, however, do not suffer from depletion effects in cold, dense regions, and so offer an invaluable tool to probe the early stages. Herschel HIFI is uniquely suited to observe the key ground-state absorption lines of four nitrogen hydride species: NH, NH2, o-NH3, and p-NH3. Our chemical models show that the line ratios are sensitive measure of density, temperature, and inferred evolutionary stage. We therefore propose observations of four very cold cores in IRDCs that we have already studied with the SMA; we supplement them with two progressively warmer IRDCs for reference with only a modest increase in time. Our goal is to quantify the early evolutionary stages of IRDC cores before they form stars, and the associated chemical activity in the cloud. We will also use the results to refine our chemical models of the nitrogen hydrides under these conditions. Our team is expert in chemical modeling of dark clouds, IRDCs, millimeter and submillimeter astronomy, and Herschel HIFI data reduction and analysis.

Lead Scientist: Howard Smith

Allocated time: 20.9 hours

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Probing short-term far-infrared variability of protostars and exploring afterglows of X-ray disk heating

Recent studies have shown that there is a surprising amount of variability on many timescales in the mid-infrared emission of young stellar objects (YSOs). Especially on short timescales of minutes to hours, mid- and particularly far-infrared variability is currently almost entirely unexplored. While such variability is probing circumstellar disks and envelopes, it is linked to physical processes on the central object. Already the earliest evolutionary stages of YSOs are also strong X-ray emitters, and one important aspect is the heating and possible eventual dispersal of circumstellar disks due to X-ray emission. Even though very important for the understanding of planet formation, this process is poorly understood. The Herschel Space Observatory offers the last possibility for the foreseeable future to explore these processes in more detail and learn about disk heating and explore the occurrence of short-term variability. Here, we propose to do both by repeated observations of the extensively studied nearby Coronet cluster in the CrA star-forming region. Five epochs of near-simultaneous XMM-Newton and Herschel observations, each about 1.5h in duration and spaced by timescales of days to weeks, are meant to explore the short-term variability and link it to the more frequently studied variability on longer timescales. During each epoch, the cluster is mapped 18 times with Herschel. The Coronet has been chosen for having YSOs that can be detected at high S/N in short periods of time while not being too crowded for the angular resolution of both observatories. By exploring far-infrared variability on timescales of several minutes to days and weeks as well as disk heating by protostellar X-ray emission, these short observations will have a unique legacy value.

Lead Scientist: Jan Forbrich

Allocated time: 7.3 hours

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Mapping Sagittarius B2 a starburst in the Milky Way's Galactic Center

We propose to use the SPIRE-FTS to map a 8.5'x8.5' (~20pc x20pc) region around Sgr B2, the only source that allows studying a burst of star formation in the center of a galaxy (GC) with high spatial resolution even using a single dish telescope (25'' = 1 pc).

Bright high-mass star forming regions do exist in the disk of the galaxy, but the specific location of Sgr B2 in the GC (where the ambient physical conditions are markedly different compared to the disk) make it the best source to compare with unresolved extragalactic nuclei (M82, the prototype starburst galaxy is ~400 times more distant and thus 25''=400 pc).

Our SPIRE-FTS pointed observations around Sgr B2(M) core and surroundings show strong dust continuum emission as well as emission lines from 12CO and 13CO rotational ladders; [NII] and [CI] fine structure lines; emission/absorption of excited H2O and NH3, and line-of-sight absorption of a variety of light hydrides (HF, CH+, CH2, OH+, H2O+, H3O+, NH and NH2) that are difficult, if not impossible, to detect from the ground. Even far from Sgr B2 star forming cores, the expected continuum and line intensities will enable us to map tens of lines over large areas in very reasonable times.

Understanding the large scale physics and chemistry of this starburst template in the GC is of great interest as recent Herschel observations are revealing similarly rich spectra in fainter galaxies where, of course, different components overlap in the beam. The proposed spectral maps and SEDs will form a large database that will be a legacy for higher angular resolution studies of extragalactic nuclei.

Lead Scientist: Javier R. Goicoechea

Allocated time: 10.8 hours

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SPIRE-FTS Observations of a Diverse Sample of Protostars and their Surroundings

We propose to observe a diverse sample of protostars with Herschel-SPIRE, selected from the DIGIT/WISH programs, to answer the key question: To what extent can we separate the system properties of a protostar (e.g. envelope/disk) from the extended properties (e.g. outflows, fast shocks)? Quantifying energetic feedback from a protostar into its surrounding environment provides a key for understanding the star formation process. Because of its simple chemistry and high abundance, CO is an ideal tracer of such feedback. We have the unique opportunity to expand a well-studied dataset of low-mass protostars with a huge range of existing observations: PACS and IRS spectroscopy, ancillary IR/optical/UV/X-ray and millimeter data, selected from the WISH/DIGIT that span a variety of bolometric luminosities and temperatures. Observations of mid-J CO lines are the missing link that we need to separate the effects of outflow from envelope emission.

Lead Scientist: Joel Green

Allocated time: 30.9 hours

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Completing the Herschel Survey of Cygnus-X

Massive stars are rare and distant. Their short-lived protostellar phases are therefore difficult to study, and the processes that produce them are not well understood. The Cygnus-X complex is one of the richest known regions of star formation in the Galaxy at a distance of ~1.3 kpc, which allows it to be studied at smaller scales and less confusion than other similarly active regions that are more distant. We have conducted a Spitzer Legacy survey of the Cygnus-X region and used the data to map the distribution of Class I and II YSOs in the complex, and have begun to study the interaction between the massive young stars and clusters of low-mass YSOs. We propose to use PACS and SPIRE to complete an unbiased survey in the Cygnus-X region to detect the intermediate to high-mass young stellar objects, pre-stellar cores, and infrared dark clouds (IRDCs) and their embedded objects. The Herschel observations, in conjunction with the existing Spitzer, near-IR, and other ancillary datasets will allow us to assemble a comprehensive picture of star formation in this high mass, extremely active complex. With the Herschel data we will 1) complete the sample of massive protostars and YSOs in Cygnus-X and construct SEDs of the objects from 1 to 1200 microns, 2) use the derived luminosities and envelope masses from the sample to construct evolutionary diagrams and test high-mass star formation models, 3) analyze the population of Infrared Dark Clouds in Cygnus-X, and 4) explore the role of massive stars in triggering star formation in surrounding clouds. The data will provide a useful resource for the study of star formation for years to come.

Lead Scientist: Joseph Hora

Allocated time: 15.5 hours

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Maddalena's Cloud: A unique Laboratory for Early Evolutionary Stages of massive GMCs?

We propose to establish the evolutionary state of Maddalena's Cloud. This region is regularly discussed as a prototype for a giant molecular cloud (GMC) in an early phase of its life. This suggestion is based on the fact that this region of about 3x10^5 M_sun is entirely devoid of embedded massive stars. Thus, this region potentially presents an ideal site to study the initial conditions for the evolution towards clouds like Orion A. This is not entirely clear, though: it has also been argued that this cloud might be at the end of its life, and is now dispersing after being "stirred up" by previous star formation. We therefore propose to execute two complementary experiments to establish the cloud's evolutionary status. Both will use wide-field parallel mode SPIRE/PACS dust emission maps. First, we will obtain the first reliable estimates for the mass of the cloud and its clumps to revise the --- presently very uncertain --- virial analysis on which suggestions for cloud dispersal are based. Second, we will search for deeply embedded young stellar objects (YSOs): if these very young (class 0-I) YSOs exist throughout the cloud, it would be hard to argue that this is a cloud in which star formation is ending. Depending on these experiments, our data will then be used to constrain the physical conditions in the early life of massive GMCs. Certainly, the properties of this cloud are unique: we only expect to find about 6 such massive clouds without O stars within 2.2kpc from sun. This is the only cloud of this sort we presently know, and so our observations will have a significant legacy value for studies of star formation.

Lead Scientist: Jens Kauffmann

Allocated time: 12.9 hours

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An accurate mass measurement for prestellar cores

Prestellar cores are crucial to our understanding of star formation. It is at this evolutionary stage that the stellar mass is set. If we are to understand the origin of the stellar IMF, we must therefore study the masses of the prestellar cores from which the stars are formed. There is currently a large uncertainty in the measured prestellar core mass that we obtain from far-IR and submillimetre observations. This uncertainty is caused by our inability to simultaneously determine the column density, temperature and dust emissivity index from photometric observations. Physical processes such as grain growth, or ice-mantle formation, which are affected by changes in density and temperature, will change the dust emissivity index. By simply taking a canonical value for the emissivity index, we cannot determine the correct mass for prestellar cores.

The SPIRE FTS allows us to break this degeneracy for the first time, and simultaneously measure the column density, temperature and dust emissivity index, and therefore determine accurate masses. We propose to map 16 prestellar cores with the SPIRE FTS, and hence generate accurate maps of their column density. We will map each core using the full FTS field of view. We will be able to determine the absolute value of the dust emissivity index, and also see whether it varies across each of the cores. We have selected cores in different environments in order to study the core-to-core, and cloud-to-cloud variations in the dust properties. We will be able use this information about the relation between the three measured parameters, to more accurately determine masses for a much larger sample of cores for which only photometric data are available

Lead Scientist: Jason Kirk

Allocated time: 11 hours

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Searching for the First XDR around a Low Mass Star Forming Region

We propose to observe the compact but well-studied protostellar core L1251B with all Herschel instruments. L1251B harbors potentially the first XDR ever isolated (there are two strong candidates) and is the only low mass source that we have an existence of the detailed maps of ice evaporation. Therefore, we propose to observe L1251B in [N II] 205.4 micron and the ground state p-H2O lines with HIFI to study the effects by high energy photons produced through the accretion process in early evolutionary stages. This will be supplemented with PACS full SED and SPIRE FTS modes. This combined data set will confirm the potential presence of the first low mass XDR. They also will allow for the only source where Herschel can connect water vapor and water ice emission to Spitzer maps of water ice absorption on equivalent spatial scales.

Lead Scientist: Jeong-Eun Lee

Allocated time: 9.3 hours

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The Galactic center as the laboratory to understand nuclear activity in galaxies (GC_JMP)

We propose to use the The Galactic center (GC) a local extragalactic laboratory to understand the chemistry and the heating mechanisms in nearby galactic nuclei. The central 30 pc region around the black hole, Sgr A*, contains all the different type of activity found in extragalactic nuclei, namely, massive stellar clusters creating large photodissociation regions (PDR), shocks, molecular clouds irradiated by strong X-rays (XDRs), and the site of Cosmic Rays (CRs) acceleration as shown by HESS. We plan to map this region with SPIRE in the high spectral resolution mode and with HIFI in selected molecular ions H3O+, OH+, and H2O+ claimed to trace XDRs and/or CRs. This unique data set will provide the possibility to understand the origin of the large column densities of this hydrides found in galactic nuclei with different type of activity and the role of the PDR-XDR-CR chemistries in their formation. The SPIRE data cubes will have a huge legacy value providing the full FIR inventory of the atomic and molecular gas across the central 50 pc of the Galaxy. We stress that only the combination of the high spectral resolution of HIFI and the spatial distribution provided the proposed mapping will have the possibility to distinguish which of the different components of the molecular gas along the line of sight correspond to the ones associated with XDRs PDRs and eventually CRs acceleration sites.

Lead Scientist: Jesus Martin-Pintado

Allocated time: 55.3 hours

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Cooling and chemistry in embedded massive protostars in the Magellanic Clouds

Stars form from contracting molecular cores, but this process relies heavily on the ability of the core to cool. This depends on chemical composition and could therefore lead to different outcomes at low metallicity. However, most of what we know about star formation is derived from studies of Galactic YSOs. Herschel provides the unmissable opportunity to extend such analysis to the low-metallicity environments of the Large and Small Magellanic Clouds (LMC and SMC), by observing the main cooling lines: fine-structure lines of oxygen and carbon, and rotational transitions of abundant molecules.

Our Spitzer Legacy Programs (SAGE; SAGE-SMC) and Herschel Key Program (HERITAGE) identified 1000s of young stellar objects (YSOs), in both Clouds. Follow-up spectroscopy (Spitzer-IRS and ESO/VLT) provided unique insight into the abundances of ices in Magellanic YSOs, revealing differences in the composition of circumstellar material at lower metallicity. Since the gas and ice phase chemistry is inextricably linked, this opens the possibility of significant variations to gas-phase abundances. Such differences could imply changes to cooling and heating rates, and consequently different star formation timescales and efficiencies.

To investigate the role of metallicity we will observe a sample of embedded massive Magellanic YSOs. We will use PACS and SPIRE FTS spectrographs to measure the strengths of key gas-phase cooling species ([OI], [OIII], [CII], H2O, CO, OH), in order to estimate temperature, density, ionization state and abundances. These observations will enable us to characterise the gas and constrain the cooling budget of the YSO envelopes. Together with our ice column density measurements, the Herschel observations are crucial to investigate how grain-surface reactions change the chemical make-up of the gas.

By comparing the SMC and LMC, and Galactic YSO samples we will assess how the chemistry, and consequently the ability of the YSO envelopes to cool, differ at sub-solar metallicity.

Lead Scientist: Joana Oliveira

Allocated time: 38.8 hours

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Probing the gas in the outer Galaxy: Molecular or Atomic?

Despite of all theoretical speculations and various observational constraints, the nature of the dark matter in the outer Galaxy is still unknown. Herschel/HIFI offers the unique opportunity to detect or set a significant upper limit to a potential component of baryonic matter in the form of cold gas, which is molecular in hydrogen, but does not form CO. Such gas can be potentially be traced through [CII] 150 um and HF J=1-0 absorption against continuum background sources. We propose a set of 7 the brightest outer Galaxy dust continuum sources, for which we will determine the positions of peak emission by PACS mapping. Deep integrations in [CII] and HF towards the 4 brightest peaks in these sources will potentially detect a cold gas component and will, in any case, give significant upper limits to its column density.

Lead Scientist: Juergen Stutzki

Allocated time: 9.2 hours

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Far Infrared Extinction (FIREX)-Mapping the Initial Conditions of Massive Star Formation

The initial conditions of massive star and star cluster formation are likely buried in the densest, coldest and most obscured regions of giant molecular clouds (GMCs). We propose to use this obscuration to our advantage by carrying out sensitive, high angular resolution 70, 100, and 160 micron PACS imaging of 10 Mid-Infrared Dark Clouds (IRDCs). Building on our experience of Mid-IR extinction (MIREX) mapping, we will apply a new analysis method of Far-Infrared extinction (FIREX) mapping to derive estimates of the mass surface densities and temperatures of massive starless cores and clumps. Compared to the 8 micron-derived MIREX maps, 70 micron-derived FIREX maps will be able to probe to at least 4 times higher values of mass surface density, into a regime >1 g/cm^2, which some theories predict is a necessary condition for massive stars to form. The high angular resolution 100 micron images are crucial for disentangling temperature variations in the IRDCs, which can mimic 70 micron absorption. This analysis will be aided by comparing with the lower resolution 160 micron images and Hi-GAL SPIRE data. It is possible that absorption at even 100 microns will be seen, picking out the very densest, coldest regions.

We note that while 70 micron (but not the crucial 100 micron) data exist for these IRDCs from the Hi-GAL survey, our proposed observations will have much improved angular resolution and flux sensitivity because of the use of a slower scanning speed. This is important to probe the highest mass surface density cores and clumps, which we know contain sub-structure down to scales at least as small as the resolution of the proposed images, ~5 arcseconds.

This project requires the stable FIR photometry that is only possible with Herschel PACS. At the same time unique science questions, resulting from probing the most extreme mass surface density regions yet studied by extinction mapping, can be carried out with a modest amount of observing time of just under 6 hours.

Lead Scientist: Jonathan Tan

Allocated time: 5.9 hours

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Characterizing the Energetics of the Youngest

We propose to observe a sample of nine very red protostars serendipitously identified in PACS observations for the Herschel Orion Protostar Survey (HOPS). In contrast to the known Orion protostars targeted in HOPS, the new sources are undetected or very faint in Spitzer 24 micron imaging of Orion. They are redder than the known Orion Class 0 protostars, and appear similar to the most extreme Class 0 objects known. These objects are likely to be in a very early and short lived stage of protostellar evolution.

With this sample, we aim to determine if the youngest protostars begin their lives in a violent energetic phase or in a more quiescent manner, slowly building their accretion and outflow power. To do this, we propose PACS Range Spectroscopy between 70 and 200 microns, observing the CO and H2O lines, and line spectroscopy centered on the 63 micron [OI] line. These far-IR cooling lines are powerful diagnostics of shock heating by outflows and radiant UV heating from accretion luminosity. Through a comparison with existing HOPS observations, these observations will be a unique window on the early evolution of outflows and accretion in protostars.

Lead Scientist: John Tobin

Allocated time: 10.6 hours

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Differential Heating of Magnetically Aligned Dust Grains

The observations proposed here are designed to search for the effect of differential heating on asymmetric dust-grains aligned with respect to an interstellar magnetic-field and heated by a localized radiation source. The grains are known to be asymmetric and aligned from observations of background starlight polarization. Modern theories on grain alignment suggest that photons from stars embedded in the foreground cloud are a key ingredient of the physical mechanism responsible for alignment. This theory predicts a relation between the grain-alignment efficiency and the angle between the magnetic field and the direction to the aligning radiation-source. This effect has been tentatively observed in a source with a very simple geometry: the aligning photons are primarily from a single localized source (i.e., a singe star) and the local magnetic-field direction is known to be fairly uniform. Such a region also has consequences for the distribution of grain heating. For example, asymmetric grains whose largest cross-sections are normal to the incident stellar radiation will reach warmer equilibrium temperatures compared to grains whose largest cross-section is parallel to that direction. This should be observed as an azimuthal dependence of the dust color-temperature. As we show in this proposal, such a dependence is hinted at in work using IRAS data at 60 and 100 micron. If this effect is real then a stronger signal is expected using longer wavelength data. Here we propose to search for this signal using Herschel/PACS photometry at 100 and 160 micron.

Lead Scientist: John Vaillancourt

Allocated time: 2.1 hours

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V838 Mon: aftermath of a stellar merger

V838 Mon is one of the most enigmatic objects observed in stellar astrophysics in recent decades. It came to attention when it underwent a powerful eruptive outburst in Jan. 2002, increasing in luminosity by a factor of 100 over a period of 3 months. Immediately following this event a spectacular light echo was formed from the outburst light reflecting off the surrounding dust. The theories that best explain the outburst are a giant star engulfing a planetary system or a merger between a very low mass star and a very young, maybe pre-main sequence low-intermediate mass star. We obtained PACS and SPIRE (and will obtain HIFI) data of the star and the surrounding dust from a GT1 proposal. From the PACS and SPIRE maps we can see that the extended emission varies with wavelegth, and hence in dust condtions. In addition, by comparing to previous Spitzer images, we can see that the morphology of the extended emission (ISM dust) and the flux of the unresolved source (new dust forming around the star) have changed between 2004, 2007 and 2011. Hence, in this proposal we are asking for 2 additional epochs of imaging, to follow the evolution of all of this dust.

Lead Scientist: Katrina Exter

Allocated time: 1.6 hours

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Search for the H2F+ ion

By using new laboratory transition frequencies of the H2F+ ion, we propose a search for the ion in interstellar space. The detection will contribute to understanding the fluorine chemistry through determined abundances of fluorine bearing molecules.

The precursor of H2F+, the HF molecule detected in diffuse molecular cloud towards W49N has a fairly large abundance of (5.5-6.9) x 1013cm-2 Since the dipole moment of H2F+ 2.79 D is large compared with 1.89 D of H2Cl+, the H2F+ ion may be detectable in such diffuse molecular clouds where H3+ is abundant.

By considering various things, we propose searches for H2F+ toward three types of sources, (1) G10.6-0.4(W31C), where HF has been detected, (2) NGC 6334I, where H2Cl+ has been detected, (3) galactic central region sources : GC IRS 21 and 2Mass J1747, where H3+ is known to be abundant. For NGC 6334I and galactic sources, HF observations are also proposed, because of no reports for HF.

Lead Scientist: Kentarou Kawaguchi

Allocated time: 4.4 hours

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Tracing the dark gas in the Perseus Molecular Cloud Complex with Herschel

Understanding the composition and physical conditions of gas in the Galaxy is crucial for understanding its structure and evolution. A great deal of information is available concerning the distribution of atomic and molecular gas but traditional tracers such as CO and HI are not able to trace regions where the gas is dense enough for H2 to exist, but where any CO and other molecules are photodissociated. These regions have been called `dark gas' (Grenier et al. 2005) and have been shown to make up ~ 30% of the molecular gas in our Galaxy. If we rely on CO, therefore, we will miss a large, important component of the molecular gas budget of the Galaxy. Our goal is to use the CII emission to trace and characterize the dark gas layer in the Perseus molecular cloud complex. Here we propose an observing program to make sparse maps of the CII emission along several cuts through Perseus allowing us to trace the transition from C+ to CI. We also propose to make maps of the CI emission over the CI to CO transition zone. We will combine the Herschel observations with already existing CO and extinction maps to determine the physical conditions in the dark gas and hence to better understand the transition from diffuse to molecular gas at the edges of molecular clouds.

Lead Scientist: Karen Willacy

Allocated time: 31.6 hours

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Tracing Galactic Metallicity with Herschel

Galactic abundances trace the processing of primordial elements by stars from the birth of the Milky Way to the present day. HII regions, because of their short lifetimes, are ideal targets for abundance determinations because they sample the current state of the interstellar medium. We propose to observe the [OIII], [NIII], and [NII] lines of 31 well-studied Galactic HII regions with the PACS spectrometer to derive the oxygen and nitrogen abundances. We hope to address two long-standing problems in Galactic abundance measurements: 1) abundances traced in the far-infrared show discrepancies with those in the optical, and 2) HII region electron temperatures derived from radio observations, which can be used as a proxy for metallicity, are not well calibrated with abundance measurements.

Lead Scientist: Loren Anderson

Allocated time: 17.2 hours

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Characterizing a Complete Resolved Star Formation Region: NGC 602 in the SMC - Beautifully Alone

We propose to map the isolated star forming region NGC 602 to characterize the temperature and density structure of the entire system. NGC 602 lies in the periphery of the Small Magellanic Cloud and is the ideal target for a complete study of a star forming region. It is distat enough (at 60 kpc) that we can map the entire region in a short time but near enough that the stellar population and the structure of the interstellar medium (ISM) are resolved. Its isolation, in the outskirts of the galaxy, means that there is virtually no line-of-site confusion, and the interstellar radiation field arises entirely from cluster stars. We have already fully characterized the stellar and protostellar content using data from the Hubble and Spitzer Space Telescopes. Now we will explore how the massive main sequence stars are driving current star formation via their influence on the surrounding ISM. We will map the photodissociation region (PDR) in the dominant [OI] 63 micron and [CII] 158 micron fine-structure cooling lines with the PACS spectrometer and in high-resolution 70 micron PACS photometry. They will allow us to probe the temperature and density structure of the PDR. We will combine these new data with our Spitzer SAGE-SMC (IRAC 3.6-8.0 micron, MIPS 24 micron) and Herschel HERITAGE (PACS 100 and 160 micron, SPIRE 250, 350, and 500 micron) broad-band imaging as well as HST optical data to integrate a picture of massive stars, star formation, and their connection with the interstellar medium on the scale of a well-defined OB association.

Lead Scientist: Lynn Carlson

Allocated time: 9 hours

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Heating and cooling mechanisms in massive star forming regions

We propose HERSCHEL observations of molecular and atomic transitions to study the heating and cooling balance in the surroundings of young massive stars. The high spectral and spatial resolution of the HERSCHEL space telescope gives an unique opportunity to observe the most relevant cooling and heating transition lines at wavelengths which are non observable from ground-based telescopes. The objective of our proposal is to understand the role of cooling during the early stages of massive star formation. Is cooling dissipating enough energy and allowing high accretion rates in young massive stars? Where is the cooling mainly taking place in massive protostars? Addressing these questions will help us to disentangle between different theories of high-mass star formation.

Lead Scientist: Luis Chavarria Garrido

Allocated time: 20.1 hours

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Disentangling energetic feedback in low-mass protostars with CO 16-15

During the earliest embedded stages of star formation the young star interacts with its surroundings through high velocity shocks and UV radiation, providing feedback on the medium from which the star is forming. At the same time, in-falling gas is heated to several 100 K by the accretion luminosity. How much energy is lost from the system through each of these processes? Is there an evolutionary trend in terms of the relative contributions from shocks and UV radiation? To address these questions and to observationally differentiate the different heating mechanisms, velocity-resolved observations are required.

Herschel-PACS has revealed that highly excited CO emission (up to J=44-43; Eup ~ 5400 K) is present towards most low-mass protostars, revealing a warm/hot component not detected previously with ISO. The PACS observations reveal directly that CO is one of the best tracers of energetic processes in protostars. To quantify emission, a model was constructed incorporating the shock- and UV-heating mechanisms. While the model is successful in reproducing observations from three sources, it also makes very specific predictions regarding the line-shape of velocity-resolved high-J CO emission. The model furthermore predicts an evolutionary sequence where CO emission in younger sources is dominated by shock heating, as opposed to UV-heating being dominant at later evolutionary stages.

To test the model and its validity for more than three sources, we propose to observe the highest excited CO line possible with HIFI, the CO 16-15 line. Velocity-resolved data will immediately allow us to quantify how much emission is caused by the different heating mechanisms. Furthermore, such data will allow us to measure the different heating contributions for this line directly, thus benchmarking our model and its underlying assumptions.

Lead Scientist: Lars Kristensen

Allocated time: 14.1 hours

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Disentangling the water chemistry of the spectacular outflow BHR71

At the earliest stages of low-mass star formation, observations show that mass accretion is associated with mass ejection in the form of collimated jets and bipolar outflows. The ejection activity can be traced as shocked regions, where shock waves originating from the central young stellar object (YSO) impact, and process the ambient interstellar medium (ISM) from which the star forms. This interaction generates molecular emission that is typical of the physical (temperature, density) and chemical (abundances) structure of the gas. Studying this molecular emission is the best way to understand the physical and chemical processes operating in shock regions.

We propose to follow the water chemistry through one of the most spectacular and best-studied outflows in the Southern sky, BHR71. Because the water abundance is very susceptible to energetic input (both through direct formation in the gas-phase and through release from ice-coated dust grains), it is one of the best shock tracers. To trace the water chemistry accurately, velocity-resolved observations are required to disentangle different excitation regimes.

Early Herschel results show that water excitation conditions resemble those of rotationally excited H2, i.e., high densities and temperatures of 300-1000 K. Currently, it is not possible to velocity-resolve rotational H2 lines. Herschel-HIFI has revealed that the water line profiles observed to date are very complex, and they look nothing like the spectra of other molecular traces. Water is therefore a unique tracer of the bulk of the shocked gas where the temperature is 300-1000 K.

Given the importance of BHR71 as the most chemically rich outflow in the southern sky, that makes it a key benchmark for outflow and shock modelling with ALMA, we propose to map this outflow in a few key H2O lines with HIFI. The maps will provide legacy-value information on water and shock excitation as a function of position and velocity throughout the outflow.

Lead Scientist: Lars Kristensen

Allocated time: 19.5 hours

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The Evolution of Massive Star Forming Regions: PACS Spectral Scans of Massive Protostars in the LMC

Understanding massive star formation is a critical piece of the star formation puzzle, yet we still do not have an unambiguous evolutionary sequence for massive stars and their environments. Herschel is the key to establishing such a critical evolutionary sequence. Probing the evolutionary sequence of massive star forming regions requires an unbiased sample of massive protostars with comparable spatial resolution. We have the largest, most complete spectroscopic sample of massive protostars: 277 sources greater than 8 solar masses observed with Spitzer in the Large Magellanic Cloud (LMC). In this proposal, we request PACS full spectral scans of 25 massive protostars (the smallest statistically varied subsample) from our survey. These 25 sources are an excellent massive protostellar laboratory as they likely span evolutionary states (from deeply embedded to revealed), are all at a common distance, are located uniformly in the LMC, have protostellar properties as derived from SED fits to the emission (giving masses, envelope properties, etc.), and exhibit other emission mechanisms (molecular gas, free-free emission, masers, etc.). We selected the 25 of our brightest sources (>20 solar masses) that dominate the emission of its clump.

In the process of establishing an evolutionary sequence for massive star formation and its environment, Herschel will provide valuable information of the protostellar regions (detections of heated envelopes, location of shocks, PDRs, etc.), and with our sample, we can observe how the spectra change throughout different evolutionary stages. Utilizing a similar approach to our Spitzer data, we will quantify spectral features through SED and radiative line transfer fitting, as well as the powerful technique of principle component analysis, which can only be accurately achieved with full spectral scans that will reap ancillary benefit for years to come.

Lead Scientist: Leslie Looney

Allocated time: 49 hours

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The physical and chemical state of high-mass pre- and proto-stellar coresidentified by the Hi-GAL survey

We propose to investigate the physical, chemical and dynamical properties of a sample of newly found high-mass pre- and proto-stellar cores identified by the ``Herschel infrared GALactic Plane Survey'' (Hi-GAL; Molinari et al. 2010). We will perform observations of the o-NH3(1_0-0_0) line (and, simultaneously, also of the o-H2O(1_10-1_01) transition) that will allow us to identify both similarities and differences between the physical and chemical conditions before and after the formation of a warm/hot source inside the dusty core identified in the SPIRE/PACS maps. Hence, these observations will improve our knowledge of the earliest phases in the evolution of high-mass stars. We will also attempt the detection of the NH(1-0) line towards a smaller sample of sources, in order to improve our knowledge of the N-chemistry during early high-mass star formation.

Lead Scientist: Luca Olmi

Allocated time: 28.5 hours

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SPECSO: Spectroscopy of Shocks in Outflows

In the early protostellar stages, fast jets powered by the nascent star, possibly surrounded by a wider angle wind, are seen to interact with the parental medium through molecular bowshocks, producing a slower moving molecular outflow cavity. The nature of the shock accelerating the outflow plays an important role in the dynamical and chemical evolution of the entrained gas.

We propose to study with Herschel the physics of protostellar outflow shocks from the observation of CO and OI lines with HIFI and PACS, in a broad sample of outflows.

These observations will permit to bring strong constraints to shock models over a wide range of parameters, and will facilitate the interpretation of current observational programs on protostellar shock chemistry and dynamics.

Lead Scientist: Milena Benedettini

Allocated time: 26.6 hours

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Investigating the origin of the intercluster medium in M15

M15 (NGC 7078) is, quite possibly, the most unusual Galactic globular cluster. It is among the most metal-poor clusters ([Fe/H] = -2.4), yet has an extremely dusty environment. M15 is home to a dusty planetary nebula (PN), one of only four in a globular cluster, and is the only globular cluster with a dusty intercluster medium (ICM). Dust is expected to collect in globular clusters when mass-losing evolved stars eject material towards the end of their lives, but it is unclear why only M15 has been able to retain this ICM. It is possible that the dust originates in the Milky Way, as either swept-up or chance superimposed material. We propose to (1) image M15 with PACS and SPIRE to determine the ICM (and PN) dust temperature and mass, and (2) obtain PACS line spectroscopy of [C II] at 158 microns to determine whether the ICM is of Milky Way origin. These observations allow us to probe the nature of the ICM material, determine how long it has been collecting (or how quickly it is being removed), and rule out whether the material is instead from the Milky Way. The results will have broad implications for the presence of ICM in other globular clusters; if the ICM is found to be of Galactic origin, it will significantly weaken the case for ICM to be present in any globular cluster.

Lead Scientist: Martha Boyer

Allocated time: 5.8 hours

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Determining the evolutionary state of the young protostar Chamaeleon MMS1

This proposal aims to determine the physical structure and evolutionary status of the relatively little-studied young protostar Chamaeleon MMS1. The central source has an unusually low luminosity and is embedded in an extremely chemically-rich parent cloud. It has been put forward as an example of a first hydrostatic core, but there is some disagreement in the literature as to whether or not it drives an outflow, and it may be undergoing episodic mass-accretion. Our proposed HIFI and PACS observations of CO and H2O rotational emission lines with a range of upper-state energies will probe the density and temperature structure of the envelope and, through radiative transfer/excitation analysis, will provide crucial information on the physical state of this object. Line profiles will be used as a probe of the envelope and outflow kinematics. OI 63 micron line mapping will provide information on the envelope energetics and will test for the presence of a hidden jet. SED measurements will help to characterise the central radiation source, disk and envelope. These combined observations are expected to improve our understanding of the earliest stages of protostar evolution.

Lead Scientist: Martin Cordiner

Allocated time: 10 hours

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HCl+ in the Interstellar Medium

The identification of the key molecules in the interstellar chlorine chemistry has required nearly three decades. Herschel-HIFI observations have revealed H2Cl+ in absorption in various Galactic lines of sight, with abundances at least ten times higher than predicted.

Recently, the proponents have tentatively identified strong absorption signatures, observed with HIFI towards two sources, with the ground-state rotational transition 2P_3/2, J=5/2-3/2 of H35Cl+, an ion that has long been predicted to be a key intermediate, together with H2Cl+, in the chlorine chemistry of diffuse clouds.

The detection, corroborated by a good agreement between observations and models of expected opacity profiles, shows, like H2Cl+, abundances in excess with respect to the expectations.

All these findings stress the need for a revision of the chlorine chemistry and of the physical parameters at play in the environments where these molecules are found. The detection of HCl+ in other sources, especially if in combination with available observations of H2Cl+, would constitute a formidable constraint for the models. The planned observations would then have an impact, not only on the chemistry, but also on our knowledge of the Interstellar Radiation Field, of the dust opacity profile and on atomic physics parameters.

We propose to observe this HCl+ transition with HIFI towards strong continuum sources for which several molecular tracers are already available, allowing us to clarify the environment where this ion is found.

The need for Herschel is extremely compelling, since the proposed transition, the only one reasonably detectable in the ISM for this species, is in a frequency range where a strong atmospheric O3 line would complicate any attempt of observation even for the Stratospheric Observatory SOFIA. This will thus be the last opportunity, perhaps in one decade or more, to observe this molecule that plays a fundamental role in the chlorine chemistry.

Lead Scientist: Massimo De Luca

Allocated time: 8.8 hours

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A prototypical jet from an intermediate-mass protostar

We ask for a joint effort of the three Herschel instruments to carry out an exhaustive spectroscopic study of the proto−stellar jet and of the molecular outflow driven by the source IRS20 (IRAS08479−4306), an intermediate-mass star precursor, in the Vela Molecular Ridge.

IRS20 constitutes a privileged target for being, at the same time, ordinary and peculiar. Ordinary because it is the most massive object at the center of a relatively small, young embedded cluster, within a cloud located on the Galactic Plane hosting Low− to Intermediate−Mass, likely quiescent, protostars. It is thus representative of the most common Intermediate−Mass star forming mode. Peculiar because the relatively short distance, the powerful, well resolved jet and outflow, the clear edge−on geometry of its disk, and the location outside the solar circle make it very easy to study.

Exploiting the spectroscopic capabilities of Herschel and the favorable displacement of the target configuration, these observations will allow a ful characterization of morphology and physical conditions of the jet and the outflow: we plan to obtain with PACS and SPIRE a wide line survey of the source surroundings, including several molecular (CO, 13CO, H2O) and atomic (OI, CII, NII) transitions, precious for deriving the physical conditions of the source vicinity, of the primary jet and of the outflowing gas; HIFI observations of the fundamental transition of the p−H2O line at higher spectral resolution are intended to resolve features that will guide in the interpretation of the lines not resolved by the other instruments. Combining these observations with data already available, from infrared to sub−mm, it will be possible to derive for the first time the mass ejection/mass accretion rate in an intermediate−mass star precursor.

The knowledge of the properties of this class of objects constitutes a crucial junction point for better understanding the modalities of the high−mass star formation.

Lead Scientist: Massimo De Luca

Allocated time: 13 hours

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CH+ tomography of the central molecular zone

Herschel observations have revaled the diagnostic capabilities of hydrides, either ionized or neutral, easily detected in absorption against intense submillimeter sources. In this project, we propose to probe the diffuse molecular gas in the Galactic Center in the CH+ and CH ground state transitions. Pioneering work by Oka and collaborators have shown the existence of warm and diffuse gas (T~300K, n ~ 50 cm-3), uniquely probed by the H3+ infrared absorption lines. CH+ absorption observed by Herschel closely mimic the H3^+ line profiles towards nearby targets. As the number of stars available for IR spectroscopy is very limited, the spatial extend and dynamics of this new component is not known. We therefore propose to use CH+ as a complementary probe of this new component, using strong submillimeter sources as background targets for absorption. The CH+ observations will be complemented by CH spectra, as CH is a known tracer of diffuse molecular gas, and by 13CH+ spectra at selected positions.

Lead Scientist: Maryvonne Gerin

Allocated time: 16 hours

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Search for CH2D+ a key reactant in interstellar chemistry

We propose to perform a deep search for the CH2D+ ion with Herschel/HIFI. This species plays a key role in interstellar chemistry, especially for deuterium fractionation at moderate temperature, but also as tracer of the symmetrical species CH3+. Because of its low dipole moment, and floppy character, its rotational transitions were not accurately known until recently (Amano 2010). Also, only two millimeter transition and one submillimeter transition are available from the ground, but in spectral regions where multiple emission lines from other species are present. Therefore, this ion escaped detection despite extensive searches by some of the proponents for over 30 years. Three of the most intense lines of CH2D+ are accessible to Herschel/HIFI in relatively clean spectral regions. The detection of CH2D+ seems therefore to be finally within reach, providing a key proof of the validity of state of the art chemical networks.

Lead Scientist: Maryvonne Gerin

Allocated time: 6.3 hours

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Supernova archaeology in Orion with chlorine isotopes

How have molecular clouds like Orion and Taurus evolved since giving birth to their first stars? The origin and evolution of molecular clouds, in particular in terms of supernova influence, can be studied through a systematic analysis of elemental isotopic composition variations in them. This approach to galactic archaeology is very promising, but little explored and so far limited to very few elements. Based on the isotopic yields of supernovae (SNe), and on existing observations, we propose that the 20 SNe that have exploded in the Orion A cloud in the past 10 Myr have substantially altered the chlorine isotopic composition and that this variation is detectable with HIFI.

The sensitivity of HIFI allows, for the first time, to perform a systematic study of sources in Orion and Taurus to map the chlorine isotopic ratio and to learn quantitatively about the Orion supernovae of the past 10 million years. This work will also contribute to our understanding of supernova-triggered star formation and ejecta-enrichment of protoplanetary nebulae.

Lead Scientist: Mihkel Kama

Allocated time: 6.8 hours

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[CII] Observations of the Perseus Molecular Cloud

Numerical simulations have suggested that giant molecular clouds (GMCs) can form from converging supersonic flows. In this scenario, the dynamics and chemistry of gas are strongly coupled and chemical processes, such as the HI-H2 and CII-CO transition, play an important role in the formation and evolution of GMCs. In particular, recent 3D magnetohydrodynamical simulations track both a detailed dynamical and chemical cloud evolution for the first time and find a significant scatter in the spatial distribution of CII and CO. This suggests that molecule formation is heavily affected by turbulence and is highly contradictory to what stationary photodissociation region (PDR) models predict. We propose to observe two boundary regions of the Perseus molecular cloud in the 158 micron fine structure line of CII using the Herschel HIFI instrument. Our proposal will test theoretical predictions from two different models (stationery vs turbulent) and address the importance of turbulence in the molecule formation. In addition, the proposed [CII] observations will allow us to explore the "CO-dark" gas in Perseus and to test the recent PDR model of the "CO-dark" gas in GMCs. The HIFI instrument will be critical to achieve our scientific goals as it provides the high enough spatial and velocity resolution to investigate the spatial distribution of CII in detail and to separate Perseus from foreground and background [CII] emission.

Lead Scientist: Min-Young Lee

Allocated time: 38.6 hours

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Shock treatment: breaking the degeneracy on the origin of water emission in protostars

What is the origin of the high excitation, mid-IR water lines in protostars? Two separate shock mechanisms have been proposed: (i) an envelope-disk accretion shock at the protostellar disk surface and (ii) shocks in outflows. Past studies with Spitzer IRS data have been unable to conclusively rule out either scenario, despite extensive study in recent literature. Doing so for a sample of the earliest protostars would further our understanding of envelope-disk-protostar dynamics and perhaps inform us of the state of a protostellar disk just after formation.

From our high resolution Spitzer IRS survey of 80 protostars in nearby star forming regions, we have assembled a sample of protostars in which strong, high excitation water lines are detected. To resolve the question of the origin of water emission, we propose full PACS spatial resolution mapping in the range spectroscopy mode of one of the most luminous water emitters in our sample.

From the PACS maps we will be able to test each shock mechanism in two ways. First, we will investigate the spatial correlation between the peaks of the water emission, continuum emission, and outflow tracers such as the [OI], CO (J > 21), and OH lines. Significant spatial offset between the water emission and the continuum, and the spatial coincidence of water emission with outflow lines would rule out envelope-disk accretion shocks. Second, we will model the combined set of PACS and IRS water lines using a large grid of non-LTE models to derive the density and temperature of the water-emitting gas. High density (n>1.0E+10 cm^-3), low temperature (T ~ 200 K) solutions would favor envelope-disk accretion shocks, while low density (n< 1.0E+6 cm^-3), high temperature (T > 1000~K) solutions would favor the outflow shocks origin of water.

Lead Scientist: Manoj Puravankara

Allocated time: 10.9 hours

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Understanding the origin of the water emission in outflows and its relation to other shock tracers

We propose to carry out PACS full scans of two bipolar outflows, HH~211 and Cepheus E, which have been identified from previous work as compact, well-defined, and possessing a clear pattern of emission stratification.

Recent observations from the WISH Key Program have shown that the water emission from nearby star-forming regions is characterized by high-velocity wings and spatial distributions indicative of outflow origin. Thanks to these observations, water has become a new and sensitive outflow tracer, albeit a special one compared to others like the standard low-J CO emission that has so far been used to characterize the large scale distribution of gas in outflows. According to our WISH observations, water traces a warmer component than the low-J CO transitions observed from the ground, and originates from gas that seems closely connected to the still-unobserved fast wind believed to underlie every bipolar outflow. Combining water and CO observations offers therefore a unique tool to study the different energy regimes of the gas in an outflow, and to infer the manner in which energy is transferred from the protostellar wind to the ambient gas. In order to better understand this connection between energy regimes, we propose to combine observations of a number of water lines and higher J CO transitions that lie in the PACS passband, and that recent observations have shown to be readily detectable.

We believe that our proposed observations will not only help better characterize two outstanding bipolar outflows, but will provide necessary clues to clarify the origin of water in other outflows and star-forming regions in general.

Lead Scientist: Mario Tafalla

Allocated time: 18.6 hours

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HYSOVAR II: Spectroscopic monitoring of far-IR-variable protostars.

We have recently obtained PACS/Photometer monitoring observations of 100 protostars in the ORION A molecular ridge as part of the program OT1_nbillot_1. We have built about 20 reliable light curves at 70 micron spanning a period of 2 months. We find that a dozen protostars exhibit measurable variability, with flux amplitude of up to 20\%, on weekly to monthly timescales. In some cases, the 160 micron light curve also shows variability with amplitude in excess of 10%. For a couple of sources, the 70 and 160 micron light curves appear to be in phase. The observed timescales are orders of magnitude shorter than the dynamical timescales of far-IR emitting material around protostars, which suggests that the mechanism responsible for the far-IR variability might originate from the inner region of the protostars. We have identified a couple of scenarios that could explain the observed far-IR variability, specifically the accretion luminosity variations originating from the inner disk that could lead to the heating of the entire envelope, and thus cause the far-IR variability. The other scenario involves a variable scale height of the disk inner edge that would cast a shadow on the outer disk and inner wall of the envelop cavity. Several of the far-IR variable protostars have already been observed with the PACS/Spectrometer as part of the HOPS program (KPOT_tmegeath_2). Some of the HOPS targets show rich spectra with multiple water and CO lines diagnostic of the activity of infalling envelopes, disks, envelope-disk accretion, and outflows. We propose a small (14.5 hours) exploratory program with the PACS/Spectrometer to monitor the physical and chemical conditions that prevail in the outer disk and envelope of a couple of far-IR variable protostars over a 2-months period.

Lead Scientist: Nicolas Billot

Allocated time: 14.5 hours

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A HIFI study to determine whether or not ammonia truly traces the densest regions of molecular hot cores

Ammonia is a widely observed astrophysical molecule and a key tracer of dense gas in the interstellar medium. Inversion transitions of ammonia have been used for many years as a temperature and column density diagnostic toward massive star forming regions. Ground based observations furthermore, point to the presence of hot, presumably dense, gas close to embedded protostars. These same data, however, lack the density sensitivity to conclusively constrain the density of the ammonia emitting gas. Thus, whether or not ammonia is truly tracing the hottest, densest gas closest to an embedded protostar is effectively unknown. The rotation transitions of ammonia, which are unavailable from ground based observatories, have the required density sensitivity to resolve whether or not ammonia truly traces the densest regions close to newly formed massive stars. We propose here to use HIFI to observe seven rotation lines of ammonia toward three molecular hot cores each with clear evidence for hot ammonia. These observations provide the only way to know if this emission also probes dense regions close to massive stars. In sum, the proposed observations require only a modest time investment and represent science that only Herschel/HIFI can do.

Lead Scientist: Nathan Crockett

Allocated time: 11.8 hours

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A Herschel survey of photodissociation regions in proplyds

Most low mass stars form near OB associations and are hence subject to the harsh feedback of massive stars. Proplyds are in this situation. They are young stars, surrounded by a protoplanetary disk which is being photo-evaporated by the far-UV (FUV) photons emitted by massive stars. This photo-evaporation process determines the mass-loss and hence lifetime of these disks, which may result in severe constraints on the planet formation timescale. The photo-evaporation flow results from the formation of a photodissocaition region (PDR) at the surface of the disk, where FUV photons heat the atomic and molecular gas. The bright far-infrared cooling lines of atomic and molecular gas, observable with Herschel, are therefore the ideal tracers to understand the mechanisms at play in the PDRs at the surface of the disks. Unfortunately, proplyds have not been observed with Herschel. With this proposal, we will obtain key cooling lines -- [OI], [CII] and high J CO-- emitted by the dense and highly irradiated PDRs of three carefully selected proplyds in the Orion and Carina Nebulae. We will then analyze these observations in the frame of PDR and disk models, in order to provide a clearer picture of the photoevaporation process. For these observations we require 10.3 hours.

Lead Scientist: Olivier Berne

Allocated time: 10.3 hours

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Measuring the CO/H2 ratio in warm gas

The CO/H2 ratio is commonly used in numerous astrophysical systems to determine the total amount of molecular hydrogen from observations of CO. However, our current knowledge of this fundamental quantity is mostly based on measurements of cold gas; for the case of hot gas we rely only on a couple of direct measurements, dating back to almost 20 years ago.

Here we propose to measure the CO/H2 ratio and its possible variations in hot gas. Our aim is to combine observations from Herschel and Spitzer tracing both molecules, in regions excited by protostelalr outflows. Current investigations show that emission from CO and H2 arises from gas at very similar excitation conditions. This fact provides strong indications that both molecules trace the same volume of gas, and therefore comparison of their column densities can directly lead to their ratio.

Lead Scientist: Odysseas Dionatos

Allocated time: 4.5 hours

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Herschel observations of the shocked gas in HH54

A shock that can be studied in detail, using a very limited amount of Herschel time, is the Herbig-Haro object HH54 located in the nearby Chamaeleon II cloud at a distance of 180 pc. The shocked region has an angular extent of roughly 30'' and is not contaminated with emission from other nearby objects. The gas, traced by H2O and CO, emits radiation predominantly in the far-infrared regime. For that reason, this program can only be executed using the instruments aboard the Herschel Space Observatory.

We propose spectroscopy of rotational H2O and CO transitions, falling in the wavelength range covered by SPIRE and PACS. These observations will allow us to stratify the shocked region in different physical/kinematical components. We will also improve our understanding of the mechanisms responsible for water production and destruction. Given the relatively large angular extent of the region, we will determine the types of shock responsible for the emission in different positions along the shocked surface. We also propose HIFI observations of selected CO and H2O transitions. A bullet feature has previously been observed in several CO line profiles. Using HIFI, we will constrain the origin and physical properties of the region responsible for this emission.

Lead Scientist: Per Bjerkeli

Allocated time: 4.7 hours

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Constraining the chemistry of water in pre-stellar cores

With this proposal, we aim to measure the water vapor abundance in two nearby dark clouds with different physical and chemical characteristics, following the successful recent Herschel results of Caselli et al. (2010; 2011, in prep.) toward the pre-stellar core L1544. These measurements are crucial to finally put constraints on poorly known parameters which regulate the chemistry of Oxygen: photodesorption and freeze-out/ desorption rates. Such parameters are at the base of astrochemistry and their large uncertainties affect our interpretation of observations toward molecular clouds and star forming regions. Herschel OT2 is a unique chance to observe water vapor in regions not affected by protostellar feedback and with simple structure, two necessary conditions to obtain unambiguous results.

Together with the existing Herschel data on L1544, the proposed observations will provide three detailed (legacy) studies aimed at exploring fundamental processes crucial for understanding Oxygen chemistry and for the overall interpretation of interstellar medium observations (including Herschel data).

Lead Scientist: Paola Caselli

Allocated time: 30.2 hours

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Unveiling the initial conditions of high-mass star and stellar cluster formation

This proposal will help answer two major open questions in the field of star formation: 1) What causes a particular region of a molecular cloud to attain high densities on the way to forming a star cluster? 2) What is the physical structure of such ``pre-star-cluster" massive clumps?

We plan to study the structure and kinematics of the envelope and the dense gas in four massive (M > 100 M_sun) pre-star-cluster clumps embedded in Infrared Dark Clouds. The selected objects have physical and chemical properties which resemble scaled-up versions of low-mass pre-stellar cores (they are cold, dense and show large abundances of deuterated molecules). They are also dark at 24&70 micron within the Herschel beam in Band 1. Therefore, they are the ideal targets where to study the initial conditions in the process of high-mass and stellar cluster formation.

We plan to simultaneosly observe ortho-H2O(1_10-1_01) (in absorption) and ortho-NH3(1_1-0_1) (in emission) to study the kinematics of the clump and the embedded dense cores. These results will also be compared to recent work toward low-mass pre-stellar cores to study how different environments affect the chemistry and the dynamical evolution of the earliest stages of star formation.

We also plan to observe CO(8-7), (9-8) and (10-9) to investigate if turbulence dissipation and shocks play an important role in the formation of dense cores and fragmentation of massive clumps. These observations are based on comprehensive MHD shock and PDR model predictions.

Lead Scientist: Paola Caselli

Allocated time: 17.8 hours

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Herschel [NII] Observations to Define the Source of [CII] Emission

The 158 micron line of ionized carbon is the strongest single long-wavelength emission feature from the interstellar medium and is the most important coolant of gas in which hydrogen is in atomic form. It is a key determinant of the evolution of these largely atomic regions into denser, cooler molecular clouds in which new stars are formed, and is widely used as a tracer of star formation in the Milky Way and other galaxies. There is, however, an ongoing, serious controversy about the origin of the [CII] emission, which has been asserted to come from the extended low-density warm interstellar medium, but has more generally been associated with the primarily molecular photon dominated regions (PDRs) intimately associated with massive, young stars. We propose a combined HIFI and PACS study of the two far-infrared [NII] fine structure lines in order to resolve the important question of the fraction of CII emission that arises in ionized gas. Specifically, we will (1) utilize the fact that due to its ionization potential NII is found only in HII regions, and with PACS 122 and 205 micron observations, determine electron densities in a sample of such regions in the Galactic plane; (2) utilize available data on radio free-free and H-alpha emission to determine the NII column densities and from this the CII column densities in the HII regions; (3) use the electron densities to determine the fraction of CII emission arising in the ionized interstellar medium. These observations will be carried out at 150 of the positions in the Galactic plane observed in [CII] by the GOT-C+ project. We will also carry out HIFI observations of 10 selected positions in the 205 micron line to determine spectral characteristics of the NII emission line, which with CII, CI, and CO profiles already in hand will serve as a further discriminant among the proposed sources of CII emission.

Lead Scientist: Paul Goldsmith

Allocated time: 64.6 hours

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First detection of 15NH and the determination of the 14N/15N in the diffuse Interstellar Medium

Understanding the origin of the elements in the Solar system is an outstanding question of modern astrophysics, cosmochemistry, and astrobiology. The origin of nitrogen, though amongst the five to six most abundant elements in our local Universe, remains poorly understood. This is due to the lack of observational constraints to nucleosynthesis models. Elemental isotopic ratio is an extremely powerful tool in this regard. A value of 440 for the 14N/15N ratio has been measured in the protosolar nebula. Similar values have been obtained in cold dense cores and in molecular clouds. Determinations of the 14N/15N ratio in the interstellar medium (ISM) are indirect and are based on abundance ratios of N-bearing molecules and their 15N isotopologues. Hence the interpretation in term of 14N/15N depends on chemical fractionation processes. Chemical models indicate that these processes strongly affect nitriles, and recent observations suggest that ammonia is probably not a reliable tracer for the 14N/15N ratio. Nonetheless, reliable methods to determine the 14N/15N ratio in cold and dense gas seem to emerge. The same is unfortunately not true for the diffuse ISM where very little is known regarding the nitrogen isotopic ratio, which should be representative of the nucleosynthesis products. One measurement in the diffuse interstellar medium (ISM) led to the small value of 240. However, this determination is based on the nitriles HCN and HC15N, and the translation into 14N/15N is strongly model-dependent. Chemical considerations show that the NH molecule is not fractionated in the diffuse gas such that the 14NH/15NH abundance ratio is the best proxy for the 14N/15N ratio. The NH molecule has been detected by Herschel/HIFI in several diffuse clouds and offers a unique opportunity to determine the 14N/15N ratio in the diffuse ISM. The proposed observations aim at the first detection of 15NH in the ISM which will allow the first robust determination of the 14N/15N isotopic ratio in the diffuse ISM.

Lead Scientist: Pierre Hily-Blant

Allocated time: 12 hours

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Probing Outflows from Massive Proto-stars with High-J CO Lines

Massive star formation remains one of the major challenges of modern astrophysics. One key ingredient which is still poorly understood are the massive outflows which are observed near 100 % detection rate toward massive protostars. The CO molecule is in principle the best probe of the flows, however most work has been done with low-J transitions which can only probe the outer swept-up layers of the flows. High-J CO transitions on the other hand probe the warm gas very near the massive protostars and are ideal probes of the physics and role of the flows in the formation of massive stars.

We propose to obtain observations in the CO(10-9) and 13CO(10-9), C18O(10-9) and the CO(16-15) lines toward a sample of 4 massive protostars which drive massive flows. We will join these data with existing lower and mid-J CO data, EVLA continuum and SPITZER/IRAC data. We will carry out radiative transfer calculations of the CO lines to determine their physical properties as function of velocity. All data together will be used to investigate the driving and collimation mechanisms and and to develop coherent models for the massive flows.

Lead Scientist: Peter Hofner

Allocated time: 10.3 hours

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Dynamics of the ultracompact HII region Monoceros R2: solving the lifetime paradox of young massive star forming region

Ultracompact (UC) HII regions represent one of the earliest phases in massive star formation. They are characterized by extreme UV irradiation (G0>10^5 Habings), small physical scales (<0.1 pc) and are embedded in dense molecular clouds. HII regions are expected to expand at velocities of the order of the sound speed (10km/s) and remain ultracompact for about 3000 years. Therefore, only a few dozen should exist in the Galaxy. However, many more UCHIIs have been observed, corresponding to lifetimes one to two orders of magnitude larger. A number of models have been proposed to solve this problem, but all have shortcomings. Our ability to test these models depends on good informations about the morphology and the kinematics of the sources.

Mon R2 is the closest ultracompact HII region (d=830 pc), the only one that can be resolved by Herschel and undoubtedly a case study. Full modeling of the CO lines previously observed with HIFI suggests that the high velocity gas arises from the layer of warm (>100 K) and dense (>5x10^6 cm-3) gas confining the UCHII region. The line profiles are well reproduced assuming that this layer is expanding at the relatively high velocity of 1.5km/s, corresponding to a lifetime of about 10^5 years. Our kinematical study of the region is however limited by the scarce HIFI observations that hinder a full 3D modeling. We propose to observe with HIFI fully sampled maps of several atomic and molecular species (CII, CO, 13CO, CH, CH+) and single pointed observations of OH+ to trace the kinematics of the different phases of MonR2.

The understanding of the dynamics and energetics of UCHII regions is key to study the feedback process of newly formed massive stars in their native molecular cloud, and therefore the evolution of giant molecular clouds. In extragalactic research, these energetic environments could dominate the physical and chemical conditions in evolved starbursts like M82 and in the most distant galaxies.

Lead Scientist: Paolo Pilleri

Allocated time: 6.7 hours

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Combining sub-mm and UV/optical absorption line

Diffuse molecular clouds were long thought to constitute a mere transitional phase between fully atomic clouds and fully molecular clouds. Because of their low densities and high UV radiation fields their were expected to be relatively devoid of molecules. However, in the last three decades, a substantial number of Galactic sightlines were observed both at high UV sensitivity with FUSE and HST and at high spectral resolution in the optical that demonstrated that these clouds had a surprisingly rich and still largely unexplained chemistry. The occurrence of absorbing clouds that intercept sight lines that contain both bright UV/optical continuum sources and bright sub-mm continuum is rare. However, we uncovered three sight lines previously observed in the UV/optical that intercept foreground clouds that can also be probed in the sub-mm. We propose to use Herschel/HIFI to obtain high-resolution spectra of HF, CH and CH+ toward these 3 sight lines. The proposed observations will gives us the unique opportunity to: (1) to calibrate the HF/H2 ratio by using "measured” FUV H2 column densities and HF with those predicted by the HF chemistry; (2) to confirm that the absorbing gas clouds probed in the sub-mm have column densities similar to those observed in the UV/optical; and (3) to estimate the H2 column using the HF measurements from HIFI toward one of our target star for which direct FUV H2 measurements are not currently available. The combined UV/optical and sub-mm observations will lead to measures of the atomic and molecular abundances in the probed absorbing gas. Since the probed material are considered clouds in transition from diffuse to molecular clouds, knowing their depletions would give an insight into the processes leading to star formation.

Lead Scientist: Paule Sonnentrucker

Allocated time: 28.3 hours

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Water emission in the shocked regions at the tips of converging filaments

The scenario of colliding flows driving molecular cloud formation (Vazquez-Semadeni et al. 2011; Hennebelle et al. 2008; Heitsch et al. 2008) is currently the most promising to explain the short star formation timescales and filamentary geometries observed (e.g. Hartmann et al. 2001). In this framework, molecular clouds are never in equilibrium state, as part of the cloud collapses while most of it disperses. High-density seeds result from the compression and gathering of material at stagnation points. Therefore, the structure and kinematics of these high-density clumps/cores and their surrounding low-density clouds may still reflect such a process. Especially, at the stagnation points (tips of the converging filaments), strong thermal fragmentation amplifies, shocks can emerge to shed the kinetic and thermal energy away from different gas flows (Heitsch et al. 2008). At the meeting layer between the converging flows, the reversed shocks will become an incubator for the cores to self-gravitate and collapse to form stars (Gong et al. 2011). Thus, evidences of converging flows can be found through a combined observations of velocity gradient/jumps toward the center, presence of protostars and signature of shock layers. We propose here to image water emission arising from the high-density ridges hosting the high-mass protostars W43-MM1 and MM2, which we have detected extended SiO emission, a hint to converging flows. Water emission is an ideal tracer to distinguish coherent kinematic patterns of converging-flows shock from the abrupt pattern of the outflow or hot core; to trace the velocity field of the converging flows from the outskirt to SiO knots to better constrain the pre- and post-shock conditions in W43, the connecting to the pre-converging low-density cloud; to determine the layer where shock terminate and leave only the fragmented dense cores hosting high-mass protostars.

Lead Scientist: Quang Nguyen Luong

Allocated time: 8.5 hours

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Resolving an outstanding problem: O2 mapping of rho Oph

The heterodyne instrument HIFI aboard Herschel is the only instrument that will be able to observe molecular oxygen from astronomical objects outside the solar system for decades to come. We encourage the HOTAC to endorse this proposal that aims to understand the formation and destruction of O2 in the star forming interstellar medium (ISM), including its important interplay with the energy balance and chemistry of the gas and dust. We select one of the very few regions where O2 has been detected with Herschel, i.e. the nearby (120 pc) rho Oph A cloud core. Its proximity allows high spatial resolution, where different physical regions are distinctly resolved, viz. dense prestellar cores, shocks due an outflow from a Class 0 protostar and an extended photon-dominated region (PDR). Of importance is to understand to what extent O2 sources are compact and dense or more uniformly extended. Mapping these regions in the 487 GHz O2 line with HIFI, and complementing with a higher excitation line toward the shock region, will yield convincing evidence which of these are the main contributors to the O2 emission and identify the major physical and chemical processes responsible for its abundance. This has been inferred to be lower by orders of magnitude than what had been predicted by early models. Oxygen chemistry forms the backbone of astrochemistry, and oxygen-bearing species generally dominate the cooling of molecular gas. This proposal seeks to understand the basic processes that dominate the major species involved in oxygen chemistry. With our proposed observing programme, in combination with adequate theoretical modelling, a long standing riddle will finally find its resolution - a true legacy of Herschel and HIFI!

Lead Scientist: Rene Liseau

Allocated time: 74.2 hours

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Unveiling the misterious case of RCW 49: a powerful HII region with associated Anomalous Microwave Emission

An increasing amount of evidence, both from radio and NIR data, seems to indicate that RCW 49, one of the most luminous and massive HII regions in the Galaxy (Paladini et al. 2003), harbors Anomalous Microwave Emission (AME).

Here, we request PACS and SPIRE mapping observations of RCW49. The proposed observations will allow us to pin down the correlation of the observed microwave excess with dust emission, hence ruling out the possibility that this can be attributed to embedded UCHII regions. In addition, they will also make it possible to perform the first accurate modeling and characterization of the properties of dust in the source, thus to identify the carrier of the AME.

Finally, the Herschel observations will have a legacy value, since, by providing the first FIR images of RCW 49, they will allow the unprecedented accurate estimate of its luminosity, mass, Star Formation Rate, as well as the possible identification of triggering sites.

Lead Scientist: Roberta Paladini

Allocated time: 1.7 hours

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HIFI Observations of the C18O and C17O J = 5-4 to 15-14

Using CO to trace the total H2 column density in molecular clouds is a common practice. This practice, however, can be fraught with difficulties. First of all, CO is often optically thick, especially towards the highest column density regions in molecular clouds (where stars are born) and so the analysis of CO emission requires complicated radiative transfer modelling. Second, the conversion from CO to H2 relies on an often unknown conversion factor and so a canonical value of 1:10,000 is usually assumed. This is especially problematic in cold (T < 20 K) dense gas, in which CO can be depleted onto dust grains. However, in warm gas surrounding massive or even low mass protostars (so called "hot cores''), depletion can be circumvented and the rarer isotopologues (13CO, C18O and C17O) are optically thin enough that they can be used as column density tracers.

We propose to use Herschel/HIFI to directly derive total C18O and C17O column densities in a number of high mass protostars. The method we will use offers an unprecedented opportunity to derive this fundamental quantity in a model independent fashion. The basic idea is simple. For an optically thin line the observed integrated emission is proportional to the column density in the upper state. This quantity can be derived without any assumptions regarding density or temperature. If you observe enough transitions of C18O one can simply estimate the total column from summing all the observed states and correcting for the missing population. In high mass star forming regions, the high densities and temperatures mean that the higher-J states can be significantly populated and an estimate of the total column density based on only a few low energy transitions can be seriously in error. With HIFI, we have access to > 7 high-J C18O transitions, and therefore we can calculate the total C18O column densities with great accuracy.

Lead Scientist: Rene Plume

Allocated time: 29.2 hours

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Variability in high-J CO lines as a proxy for variable accretion in embedded protostars

Embedded protostars are underluminous compared to model predictions of constant mass accretion rates from the envelope to the young star. This "luminosity problem" can be explained by episodic accretion: most of the mass is accreted in short bursts, so that most of the protostars are observed in a quiescient, low-luminosity state. The timescale between such accretion bursts is on the order of 10^4--10^5 yr. Smaller brightness variations (factors of at most a few) are seen on shorter timescales (days to years) in the more evolved T Tauri phase. Similar small-scale, short-period variations likely occur in the earlier embedded phases, but they are difficult to observe because of the high extinction through the envelope at UV to IR wavelengths. We propose a novel way of studying variable accretion in the embedded phase by obtaining a second epoch of Herschel-PACS data on rotationally excited CO lines in a sample of 21 previously observed embedded protostars. The high-J CO lines (upwards of 10-9) originate in UV- and shock-heated gas in the inner ~1000 AU of the envelope. The UV field and the shock strength are both tied strongly to the accretion rate, so variability in the high-J CO line fluxes can be used as a proxy for variability in the accretion rate. A second epoch of data on the CO 14-13, 16-15, 24-23 and 30-29 lines will reveal to what extent embedded protostars show variable mass accretion rates on timescales of up to a few years.

Lead Scientist: Ruud Visser

Allocated time: 10.3 hours

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Hot water in hot cores

As matter flows from the ice-cold envelope onto a forming protostar, it heats up from temperatures of 10 K to more than 100 K. The region where the temperature exceeds 100 K (the hot core or hot corino) is where the molecular envelope connects with both the seedling circumstellar disk and the bipolar outflow. As the envelope contracts from larger scales, a lot of material passes through the hot core before accreting onto the disk. The hot core is therefore a crucial step in establishing the physical and chemical properties of planetary building blocks. However, little is yet known about hot cores. How large and how massive are they? How hot are they? Are they exposed to strong UV or X-ray fluxes? We propose the rotationally excited 3(12)-3(03) line of H2-18O at 1095.6 GHz (E_up = 249 K) as a novel probe into the properties of hot cores. This line was detected as a narrow emission feature (FWHM ~4 km/s) in a deep integration (5 hr) in the Class 0 protostar NGC1333 IRAS2A. Comparing the line intensity to radiative transfer models, we find a tentative H2-16O hot core abundance of 4x10^-6. This is a factor of 50 lower than one would expect from simple evaporation of water ice above 100 K. Why is the hot core of IRAS2A so much "drier" than expected? Is most of the water destroyed by UV photons and/or X-rays? We propose to measure the water abundance in the hot cores of a sample of five additional Class 0 and I protostars by obtaining deep integrations of the 3(12)-3(03) lines of H2-16O and H2-18O. This mini-survey will reveal whether NGC1333 IRAS2A is unique in having a "dry" hot core, or whether "dry" hot cores are a common feature of low-mass embedded protostars. If they are a common feature, it means they are a more hostile environment than previously thought, with high fluxes of destructive UV photons and X-rays.

Lead Scientist: Ruud Visser

Allocated time: 19.9 hours

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Measuring chlorine depletion in low mass star forming regions

Dust particles represent only about 1% of the mass of the Interstellar Medium but play an important role in star and planet formation. Maybe one of the most important aspects is that the process of forming planets from centimetre grains depends on the chemical composition of those grains. Chemical models, which (indirectly) take into account this composition, are hence performed to investigate the evolution from the dense prestellar core to the protoplanetary disk. However, the results of these models strongly depend on the assumed gas-phase elemental abundances. Many authors have been measuring these abundances in the diffuse interstellar medium (densities < 10 cm^-3) and have observed a gradual depletion (onto grain mantles) of gas-phase elements with the density of the clouds. However, to properly model the protostellar evolution, it is necessary to obtain a measurement of elemental depletion in clouds of much higher densities (> 10^4 cm^-3). Due to its simple chemistry, we propose to use chlorine for this purpose. We will target low-mass protostars, in which the central region shows temperatures large enough for grain mantles to be completely evaporated. Hence all the atomic Cl that was depleted onto grains returns to the gas-phase where it undergoes ion-neutral reactions to form HCl. Therefore we can use HCl as a tracer of Cl. Based on HCl observations of the low-mass protostar IRAS16293-2422, obtained as part of the Guaranteed Time Key Program CHESS, we found that observations of the (2-1) and most importantly of the (3-2) HCl transitions are crucial in addition to the (1-0) line. We therefore propose to observe these three transitions of H35Cl, as well as H37Cl (1-0) and (2-1) (for opacity determination) at no extra cost, with the HIFI instrument in a selection of five low-mass protostars in order to put additional constraints on the fraction of the cosmic Cl in volatile form, thereby improving the accuracy of chemical models and our understanding of star and planet formation.

Lead Scientist: Sandrine Bottinelli

Allocated time: 18.3 hours

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The Herschel far-infrared view of a shell bubble inflated by Cygnus X-1 microquasar jets

Radio lobes and hotspots provide invaluable diagnostics of the relativistic jet power and content in active galactic nuclei. Likewise, the interstellar medium should behave like a calorimeter for microquasar jets. However, signatures of the interaction of microquasar jets with the ISM are both fainter and on comparatively larger scales than for AGN jets. We propose here far-infrared (FIR) Herschel/PACS and SPIRE wide-field imaging observations to map the surrounding environment of the microquasar and supergiant X-ray binary Cygnus X-1. This will allow us to detect the presence of filamentary structures associated with shell shock ionisation. Measuring the shell distribution, size and speed will constrain the average jet power and provide information on the fraction of the accretion power dissipated by ejection instead of radiation. These observations, by bringing a case study of shock collisions of relativistic jets with the ISM, close to a star formation region, and potentially triggering star forming processes, will strongly contribute to the Herschel legacy.

Lead Scientist: Sylvain Chaty

Allocated time: 2.5 hours

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Measuring the Emissivity Index of Dust in a Starless Core on the Brink of Star Formation with the SPIRE/FTS

Maps of the thermal emission from dust in nearby star-forming regions have revealed an apparent similarity between the mass distributions of dense cores (CMF) and the stellar initial mass function (IMF). Deriving the mass of a core from measurements of dust emission is not straightforward, however. The primary difficulty comes from uncertainty in the dust emissivity, and in particular the slope of the dust emissivity at long wavelengths (the emissivity spectral index). Ground-based observations of the continuum emission from cores suffer from atmospheric contamination, so the best way to derive the emissivity spectral index is from space-based observations. Through our successful OT1 proposal (OT1_sschnee_1) we are mapping the spectral energy distribution (SED) of 11 cores in nearby molecular clouds using SPIRE/FTS to determine their masses accurately and constrain the emissivity spectral index of the dust emission. Now we propose to add a unique and interesting target to our sample and acquire similar data toward L1689-SMM16, a starless core newly identified to be on the brink of star formation. These observations will be supplemented with recently acquired GBT ammonia observations of the same region to break the degeneracy between temperature and the emissivity spectral index inherent in SED fits. The proposed data will enable us to derive much more accurate core masses, test the similarity between the CMF and the IMF, and search for variations of the dust properties with environmental factors such as temperature and density.

Lead Scientist: Shadi Chitsazzadeh

Allocated time: 0.5 hours

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Hi-GAL2pi. Completing the Herschel infrared Galactic

Hi-GAL2pi will complete the 5-band far-IR survey of the Galactic Plane (GP), using PACS and SPIRE in pMode to map the two Galactic longitude areas that are not covered by the Hi-GAL KP nor its OT1 extension to the outer Galaxy. These two ~60° longitude-wide slices centered toward the cardinal directions l=90° and l=270° include critical regions with uniquely favourable observing conditions found nowhere else in the Galaxy: a) the longest available panoramic view of the Persus Arm, which is the arm with the least foreground contamination from the sun's viewpoint; b) the largely unexplored inter-arm region between the Persus and Carina Arms that spans most of the l=270° slice, that alone can be observed relatively free of confusion from our vantage point. The complete census of temperature, mass, and luminosity of filaments, clumps, cores and YSOs in these two regions will provide a spatially resolved measurement of the arm/inter-arm contrast in star formation rate (SFR) and efficiency (SFE), as well as a panoramic and unconfused view of the SFR and SFE along a full spiral arm extending from the Molecular Ring to the outer co-rotation Galactocentric radius. These observables, not accessible in the GP area covered in Hi-GAL KP or OT1 programs, will uniquely enable the critical steps in our understanding of the mechanisms responsible for the assembly, formation and fragmentation of the HI superclouds and the molecular clouds on spiral arms, and thus lay the foundations for a predictive global model of star formation in the Galaxy, that may serve as a template for Extragalactic studies. The completion of the Herschel Galactic Plane survey will establish a unique legacy that will be a keystone for all future Galactic and much extragalactic research, with data products that will be mined for decades by future generations and used for research not yet envisioned, with rich potential for serendipitous discoveries. Given our demonstrated community-oriented approach, we again waive our proprietary period.

Lead Scientist: Sergio Molinari

Allocated time: 257.8 hours

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Probing Star Formation in the Extreme Environment of Onsala 2

One of the closest massive star-forming regions known, and surprisingly one of the least studied, is the Onsala 2 (ON2) complex in Cygnus at d = 1.2 kpc. The ON2 region shows numerous signs of active high-mass star-formation including OH masers, compact and ultracompact HII regions, and luminous molecular outflows. A unique feature of ON2 is that it harbors the rare and remarkable Wolf-Rayet star WR 142, a strong UV source whose hypersonic wind is driving shock waves throughout the region. We propose to conduct the first comprehensive IR study of ON2 using PACS and SPIRE, supplemented by existing Spitzer IRAC/MIPS data and high resolution Chandra X-ray data. This study will build on (and complement) our X-ray study of ON2 already in progress. Our primary goal is to develop a broad picture of how star-formation is proceeding in ON2 and to identify environmental factors that may be affecting it (e.g. ionization and shocks associated with HII regions and WR 142). We will identify and classify all IR-excess YSOs, including the population of embedded sources and low-mass YSOs about which little is yet known. We will determine if filamentary structures containing YSOs are present and will use information on the spatial distribution of YSOs relative to strong ionizing sources to search for evidence of triggered star formation. Aperture photometry will provide information on the physical properties of individual YSOs and a dust temperature map of ON2. Steep temperature gradients are expected near strong ionizing HII regions, one of which is known to be a source of hard diffuse X-rays. We also propose to obtain targeted SPIRE FTS spectroscopy of the massive YSO IRAS 20198+3716 to determine properties of the gas in its vicinity.

Lead Scientist: Stephen Skinner

Allocated time: 2.9 hours

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Hyperfine structure resolved OH map of the high-mass star-forming region W3 IRS5

Water is one of the most important molecules in star-forming regions because of its high abundance. However, the relative importance of its various formation and destruction routes is not well understood. OH is a key species in the H2O chemistry as it is closely linked to the H2O formation and destruction through OH + H2 <-> H2O + H. Herschel offers a unique opportunity to study the H2O reaction network, because OH cannot be observed from the ground. The first hyperfine structure resolved OH far-infrared spectrum from the high-mass star-forming region W3 IRS5 was obtained with HIFI previously. OH emission was expected to arise from the innermost parts of the protostellar envelope. The spectrum however showed a strong outflow component. From the hyperfine resolved OH we could derive physical properties of the emitting gas and the comparison with H2O constrained the chemistry: the gas-phase OH and H2O abundances are consistent with photodesorption from grain mantles in the outer envelope. In the inner envelope almost all OH is driven into H2O, consistent with high-temperature chemistry. To obtain the lacking spatial information on the OH distribution in W3 IRS5, we propose to map W3 IRS5 with HIFI. From the map we will learn how the relative contributions from the outflow and the envelope and the H2O chemistry change with position. HIFI is crucial to resolve the hyperfine structure OH, allowing us to derive the excitation temperature, column density, and optical depth. The second goal is to test predictions from theoretical calculations of the OH with H2 collision rates. A strong asymmetry, caused by an asymmetry in the collision coefficients, in the line strengths of the two OH line triplets belonging to the same rotational states is predicted by theory. We propose to observe a second OH line triplet, which is complementary to the one from the previous observation, towards the center of W3 IRS5. Comparison of the two triplets will allow us to test the predictions and to validate the rate coefficents.

Lead Scientist: Susanne Wampfler

Allocated time: 1.7 hours

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PACS and SPIRE Observations of the NGC 281 Star Forming Region

NGC 281 is a remarkable laboratory for studying the complex interactions between a massive star and a molecular cloud. Chandra and Spitzer data combined with ground-based data show a partial bubble of cold molecular gas surrounding an HII region. Within the HII region, an elongated bubble of 10~MK gas is detected by Chandra. We propose PACS and SPIRE observations to map the distribution of dust and protostars in NGC 281. The distribution of protostars will be used to search for triggered star formation at the cloud/HII region interface and to examine evidence for two modes of triggered star formation. The dust distribution will be used to map the interaction of the molecular cloud and the HII region. Of additional interest is the presence of dust toward the hot, X-ray emitting gas. Such dust may facilitate charge-exchange with ions giving rise to high energy lines observed in the hot plasma.

Lead Scientist: Scott Wolk

Allocated time: 9 hours

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The Evolution of Dense Cores to Protostars

Low mass stars form in dense cores of gas and dust. Many details of how this happens are unclear. Sensitive continuum mapping observations at wavelengths that sample the peak of their SEDs (100-300 microns) are needed, for a large ensemble of cores, in order to investigate dense core evolution. Isolated dense cores are the best place to study core evolution, as they are free of the confusing effects of star formation in large clouds and clusters. We propose to map, in the continuum with PACS and SPIRE, a large ensemble (of order 150) of isolated dense cores spanning a range of peak extinctions and star formation activity. By combining these data with Spitzer and submm continuum and molecular line observations, we will determine the physical, dynamical and chemical state of each core. These results will enable us to investigate many questions relating to how dense cores form and evolve toward star formation.

Lead Scientist: Tyler Bourke

Allocated time: 28.5 hours

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Lonely Cores: Star Formation in Isolation

Low mass stars form in dense cores of gas and dust. Many details of how this happens are unclear. Sensitive continuum mapping observations at wavelengths that sample the peak of their SEDs (100-300 microns) are needed, for a large ensemble of cores, in order to investigate dense core evolution. Isolated dense cores are the best place to study core evolution, as they are free of the confusing effects of star formation in large clouds and clusters. We propose to map, in the continuum with PACS and SPIRE, a carefully selected group of isolated cores with low peak column density (about 30 cores), to study the earliest stages of core evolution. By combining these data with Spitzer and submm continuum and molecular line observations, we will determine the physical, dynamical and chemical state of each core. These results will enable us to investigate many questions relating to how dense cores form and evolve toward star formation.

Lead Scientist: Tyler Bourke

Allocated time: 10.5 hours

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A diagnostic study of shocks of converging flows seen within the DR21(OH) clump

DR21(OH) is the most massive protocluster within 3 kpc and therefore serves as a perfect laboratory to study the onset of high-mass star-formation. Recent high-angular resolution observations identified flows of cold dense gas from parsec to sub-parsec scales associated with the sites of high-mass protostars similarly as it is predicted by the dynamical, fast star-formation scenario. It is however observationally challenging to find direct evidence and proof for the converging flow model. Our group has identified the most promising potential sites in the Cygnus-X complex where the shocks associated with these converging flows could be found. Here we aim for a detailed study of typical shock tracers (i.e.OI, OH and H2O lines using PACS and SPIRE spectroscopy) to reveal the signatures of the shocks as well as to study the CO ladder to constrain the excitation conditions at these sites. We also target a water line with HIFI to obtain velocity resolved spectra of the proposed shocks. This will provide a comprehensive view on these shocks and test the converging flow scenario. Herschel is the only opportunity to extensively study these molecular tracers and could provide the first direct evidence for dynamical star-formation models.

Lead Scientist: Timea Csengeri

Allocated time: 3.8 hours

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Discovering Sgr A* in the far infrared with Herschel

We propose to observe Sgr A*, the super massive black hole in the Center of the Milky Way, with Herschel/PACS. This will yield the first detection of Sgr A* in the far infrared. This is possible despite the large background because Sgr A* is a variable source. Its emission is known in the radio to sub-mm, near infrared and in the X-rays. Sgr A* shows a steady (quiescent) emission component with small variations and in addition occasional large amplitude flares. The quiescent emission is reaches its maximum in the sub-mm. However, the extent of this bump (caused by synchrotron radiation from thermal electrons) is not clear due to missing observations in the far infrared. The proposed observations would fill that gap. The emission in flares is most prominent in the near infrared and X-rays where the variable emission is simultaneous. The far infrared can provide decisive evidence for the true link between the near-infrared and sub-mm emission: whether it is one of these two cases or some other scenario. For answering these two questions we ask for time resolved photometry of Sgr A* with Herschel/PACS.

Lead Scientist: Tobias Fritz

Allocated time: 40.1 hours

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Herschel mapping of the Vela-D star forming region

We ask to exploit the Herschel unprecedented angular resolution and sensitivity in the critical range 70-500um, to investigate the early phases of star formation in a nearby (700pc), low- to intermediate-mass star forming region in the plane of the Galaxy, i.e. the Vela Molecular Ridge , cloud D (4.5 x 2 squared degree). We ask PACS and SPIRE in parallel mode (9.9 h) to : 1) define a robust sample of starless/protostellar cores; 2) define the census of the very young stellar population; 3) derive the Initial Mass Function and the Core Mass Function of the region up to sub-solar masses, and find the relationship between these two fundamental quantities.

Lead Scientist: Teresa Giannini

Allocated time: 9.9 hours

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Detection of 13CCC in star forming regions

Study of carbon chain molecules in the ISM is of great importance owing to the ubiquity of these molecules and their potential role as the building block of larger molecules or as products of photo-destruction of larger molecules. However the formation mechanism of even the simplest linear carbon chain molecule is still not well understood. The isotopic abundance ratio of C3/13CCC is believed to be an important probe for the chemical routes for the formation of C3, which involve C+. Using HIFI/Herschel C3 has for the first time been detected in the warm envelopes of hot star forming cores (Mookerjea et al. 2010). This has provided access to a much larger column density of C3 than was previously possible with optical and/or mid-infrared studies of C3 in diffuse clouds. The larger column density of C3 implies a higher probability of detecting its rarer isotopologue 13CCC. This detection coupled with the recent success of the Cologne spectroscopy group in identifying the 13CCC molecule in the laboratory and accurate determination of frequencies of several nu2 bending mode ro-vibrational transitions in the far-infrared has set the stage for a search for 13CCC in the interstellar space. We propose to obtain deep integrations of the brightest of the spectral lines for 13CCC towards two very strong continuum sources in both of which C3 has already been clearly seen in absorption.

Lead Scientist: Thomas Giesen

Allocated time: 9.6 hours

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Ascertaining the Origins and Evolution of the Mid/Far-Infrared Luminosities of Classical Novae

Classical novae (CNe) are cataclysmic variables that undergo thermonuclear runaways every ~ 10,000 yr. During these events, they have luminosities that can exceed the Eddington luminosity for a solar mass object. This enormous luminosity drives an expanding fireball outwards at high velocity. As the dense gas clumps in this fireball cool, dust can form. About one third of all CNe form dust. Thus, it may not be surprising to find that many dusty CNe were detected by IRAS. But analysis of those detections showed that if the dust shells of those CNe had expanded freely, they would have been much too cold and faint to have been detected by IRAS given the luminosities of the post-outburst systems that are their illuminating sources. What then, is the explanation for the high IRAS detection rate of CNe? Perhaps the expanding dust shells interact with material in a pre-existing circumstellar shell surrounding these objects, and are heated through kinetic processes. Alternatively, maybe the IRAS detections were due to line emission from highly overabundant species in their gaseous ejecta. It is hard, however, to ionize this material given the observed quiescent luminosities of CNe. Since the time of IRAS, two other mechanisms have been employed to explain the mid/far-IR excesses of cataclysmic variables: circumbinary disks, and synchrotron emission. Either of these two sources appear to be more viable explanations for the IRAS detections of CNe. We propose to use Herschel PACs to obtain 70 and 160 micron photometry, and SPIRE to obtain 250, 350, and 500 micron photometry of seven dust-producing CNe spanning a wide rage of times since outburst to understand both the nature of their mid/far-IR emission, and how this emission evolves with time. Our program requires 5.9 hr.

Lead Scientist: Thomas Harrison

Allocated time: 5.9 hours

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SPIRE and PACS Imaging of the Unsual Giant Molecular Cloud G216 (Maddalena's Cloud)

G216 is a unique giant molecular cloud distinguished by its large mass (10^6 Msun), lack of massive star formation, sparse population of low mass stars and protostars, and cold gas temperatures. We propose PACS and SPIRE mapping of this region to map the structure of the cold dust (and gas) in the cloud and search for protostars within the cloud. With this data we will use G216 as a laboratory for studying the dependence of the rate and effiency of star formation on the density and temperature of the molecular gas. We will search for column density thresholds and Schmidt-like star formation laws previousy reported in other more active star forming clouds; with G216 we can look for thresholds and star formation laws in a unique environment provided by a massive cloud with relatively low gas column densities, low star formation rates, and low kinetic temperatures. We will also compare the properties of the protostars in G216 to those in warmer, more active clouds to assess the influence of the gas conditions on protostellar evolution

Lead Scientist: Tom Megeath

Allocated time: 4.8 hours

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Diffuse gas and high ionization rate near the Galactic center

We use far-infrared rotational spectra of OH+, H2O+, and H3O+, which we collectively call hydroxyl-ions, to study diffuse gas and high ionization rate in the Central Molecular Zone of the Galactic center. Such study has been reported by using infrared spectrum of H3+, but the observable sightlines have been limited to few bright dust-embedded stars with smooth continuum. Taking advantage of the nearly continuous far-infrared dust emission near the Galactic center, we can probe the environment systematically and extensively.

It was found last year that the velocity profile of H3+ observed by ground based infrared telescope and that of H2O+ observed by the Herschel Observatory toward Sgr B are remarkably similar suggesting that they are probing similar environment. Hydroxy-ions and H3+ probes similar environment but their properties are complementary. H3+ determines temperature and density directly while the three hydroxyl-ions provide the fraction of H2 which cannot be determined from H3+, an important parameter to determine the ionization rate. They both determine the ionization rate.

27 bright targets selected from the Herschel SPIRE 250 μm image will be used as radiation source. Four of them are sightlines in which H3+ have been observed. Such observation will establish correlation between the hydroxy-ion and H3+. The rest of the 23 targets are to fill the gap and extend the region of the observation. The H3+ observations have been limited very close to the Galactic plane but we can probe high altitude using the hydroxyl-ions.

The extended observation will allow us to discuss the relation between the high ionization rate and high energy astrophysical activities such as the cosmic ray population, supernova remnants and X-ray and γ-ray emissions. The observed high temperature and ionization rate have implication on the slow star formation and top heavy initial mass function reported in the region.

Lead Scientist: Takeshi Oka

Allocated time: 6.8 hours

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PACS spectroscopic obervations of the shocked regions in the Galactic plane

We propose to make PACS spectroscopic observations of the regions on the Galactic plane, where strong [CII] emission is suggested to be present by AKARI all-sky survey observations. These regions are thought to be excited by interstellar shocks. The proposed observations will allow us to obtain a general view of the role of shocks in the interstellar medium and their effect on the dust processing.

Lead Scientist: Takashi Onaka

Allocated time: 27.8 hours

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Atomic and Ionic Spectral Line Probes of Protostellar Jets and Outflows

We propose to resolve the origin of the strong [OI] 63micron and [CII] 158 micron emissions, within protostellar jet-outflow sources, detected by ISO LWS, and use it as a diagnostic of the shock conditions. Both [CII] and [OI] emission are useful diagnostics of the postshock gas, and [OI] is an efficient coolant in the high velocity dissociative shocks. Though [CII] is less important as a coolant in the shocks, its high intensities make it an ideal probe for Herschel because of HIFI’s high spatial and velocity resolution which can answer where, within a jet and wind driven environment filled with shocks and outflow cavities, such strong emissions originate. In this proposal we use the PACS and HIFI spectral line mapping of shocks in 4 representative jet/outflow sources to study their spatial and velocity structures and their association with the jets and outflows, and the entrained regions. All these jet outflow targets have strong [OI] and [CII] detections by ISO LWS and contain atomic and ionic and molecular hydrogen jets; two were selected for the presence of wide angle outflow cavities; and two were selected for their star-forming and external FUV environments. These observations will characterize the components of the [OI] and [CII] associated with the shocks and outflows and serves as templates for understanding the ISO detections in a larger sample and using them as probes in future.

Lead Scientist: Thangasamy Velusamy

Allocated time: 28 hours

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Probing Galactic Spiral Arm Tangencies with [CII]

We propose to use the unique viewing geometry of the Galactic spiral arm tangents , which provide an ideal environment for studying the effects of density waves on spiral structure. We propose a well-sampled map of the[C II] 1.9 THz line emission along a 15-degree longitude region across the Norma-3kpc arm tangential, which includes the edge of the Perseus Arm. The COBE-FIRAS instrument observed the strongest [C II] and [N II] emission along these spiral arm tangencies.. The Herschel Open Time Key Project Galactic Observations of Terahertz C+ (GOT C+), also detects the strongest [CII] emission near these spiral arm tangential directions in its sparsely sampled HIFI survey of [CII] in the Galactic plane survey. The [C II] 158-micron line is the strongest infrared line emitted by the ISM and is an excellent tracer and probe of both the diffuse gases in the cold neutral medium (CNM) and the warm ionized medium (WIM). Furthermore, as demonstrated in the GOTC+ results, [C II] is an efficient tracer of the “dark H2 gas” in the ISM that is not traced by CO or HI observations. Thus, taking advantage of the long path lengths through the spiral arm across the tangencies, we can use the [C II] emission to trace and characterize the diffuse atomic and ionized gas as well as the diffuse H2 molecular gas in cloud transitions from HI to H2 and C+ to C and CO, throughout the ISM. The main goal of our proposal is to use the well sampled (at arcmin scale) [C II] to study these gas components of the ISM in the spiral-arm, and inter-arm regions, to constrain models of the spiral structure and to understand the influence of spiral density waves on the Galactic gas and the dynamical interaction between the different components. The proposed HIFI observations will consist of OTF 15 degree longitude scans and one 2-degree latitude scan sampled every 40arcsec across the Norma- 3kpc – Perseus Spiral tangency.

Lead Scientist: Thangasamy Velusamy

Allocated time: 33.5 hours

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Probing the Hidden Molecular Gas in HVCs with [C II]

The High Velocity Clouds (HVCs) detected in HI are an important constituent of the infalling gas fueling the Galaxy. Our understanding the HVCs is limited by the use of HI as the only velocity resolved gas tracer. One of the critical issues is the temperature and densities of these HVCs, and whether there is H2 molecular gas in them. The [C II] 158-micron line is the strongest infrared line emitted by the interstellar gas and is an excellent tracer and probe of both the diffuse gas in the cold neutral medium (CNM) and the warm ionized medium (WIM). Members of our team have used [CII] is an efficient tracer of the “dark H2 gas” in the clouds in the Galactic plane that are not traced by CO or HI. Here we propose HIFI [CII] observations of the HVCs in Complex C observed by Spitzer, and in the DRACO and UMAEAST fields, selected from the early results of diffuse interstellar dust observations by Planck. It is important to search for the hidden gas using other tracers such as [C II] because it gives us information about the transfer of mass from the halo to the disk. In addition to the C+ emission in the HVCs, our observation will characterize the WIM and the CNM clumps in a few intermediate velocity clouds (IVCs) and high latitude local HI gas with high sensitivity.

Lead Scientist: Thangasamy Velusamy

Allocated time: 3.5 hours

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Dynamics of Giant Magnetic Gas Loops and Their Connection to the CMZ in the Galactic Center

Understanding the mass transfer and dynamics among the Galactic Center, the disk, and the halo of the Milky Way is fundamental to the study of the evolution of galaxies and star formation. Recently several giant loops of molecular gas (GML) have been found in the Galactic Center from CO maps, which are likely the result of the magnetic Parker instability. There is new evidence of a possible connection between these loops and the Central Molecular Zone as shown in a sparse [CII] sampling made by the Herschel Key Project GOT C+. Here we propose to map various features of the GMLs and the interface region in [CII] with HIFI. We will also map the foot points of the loop, which are thought to be highly shocked regions, in the ortho 110-101 line of water, which is a known shock tracer. With this data we will characterize different ISM components and their flow among these Galactic Center features.

Lead Scientist: William Langer

Allocated time: 27.9 hours

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Si and Fe depletion study in both ionized and PDR gas of Galactic star-forming regions combined with Spitzer

We propose PACS line spectroscopy observations as well as partly photometry to estimate the Si and Fe gas-phase abundance with a clear separation of the contribution from the ionized and photodissociation region (PDR) gas combined with Spitzer/IRS observations (GO2; ID200612) in 7 Galactic star-forming regions. With Spitzer/IRS observations the Si and Fe gas-phase abundance has been examined and the depletion of Si is shown to be clearly larger than that of Fe, but the attribution of the origin of [SiII] 35 micron and [FeII] 26 micron are very limited and individual gas-phase abundance has large uncertainties. In this proposal, we plan to separate two gas-phases of the ionized and PDR gas from taking the correlation of the [SiII] 35 micron and [FeII] 26 micron emission with [NII] 122 micron and [OI] 146 micron. The electron density derived from [NII] 122 micron / 205 micron and the PDR properties derived from [OI] 63 micron and 146 micron, [CII] 158 micron, and the total far-infrared flux will be used to convert the line intensity ratio into the ionic abundance ratio.

Lead Scientist: Yoko Okada

Allocated time: 10.4 hours

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Multi-epoch observations of IC 348: Using Far Infrared Variability to ConstraintheDust Structure in Young Stellar Objects

There is growing evidence that the star formation process is in fact highly dynamic, on timescales from days to centuries. The temporal variability is a new and powerful diagnostic tool to study Young Stellar Objects (YSOs). Depending on the time scale of the variability in the mid and far infrared we can learn about different physical mechanisms shaping their structure and dynamics. Here we propose to extend our near and mid infrared study of variable YSOs in the young open cluster IC 348 to the far infrared (70 and 160 micron) using Herschel/PACS. We will constrain the frequency of far infrared variability and compare the observed time dependent behavior with protostellar and disk models to understand its origin. Possible mechanisms include fluctuations in the accretion luminosity, or echoes of inner disk structural changes projected onto the infalling envelope or flared outer disk surface. Our sample in IC348 covers a large part of the evolutionary sequence of YSOs from class I sources to transitional disks. The cadence of the requested observations allow us to study variations on time scales from days to months that could be extended to several years using our Spitzer/MIPS data. This OT2 proposal is an essential complement of our GT2 program covering one visibility epoch,

Lead Scientist: Zoltan Balog

Allocated time: 4.4 hours

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