Observing Programmes: Planetary Systems

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Guaranteed Time (Key Programmes)


Stellar Disk Evolution

This project apply the full power of Herschel to investigate the properties of six nearby circum-stellar disks. The spatial resolution of Herschel allows us to trace how the dust properties change from regions close to the central star to regions further out. Vega, one of the program stars, has a dust ring at a distance of 90 AU from the star, and this ring is clearly resolved by Herschel. Herschel spectroscopy shows the gas component for the youngest of these disks, that around beta Pictoris, and the amount of different gasses will give clues to their origin (either being released from the numerous comet-like objects approaching the star or as a result of solid body collisions).

Lead Scientist: Göran Olofsson (Stockholm Observatory)

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Structure and Evolution of Disks around Brown Dwarfs and Very Low Mass Stars

This project will use PACS to observe young brown dwarfs and stars right on the lower mass limit of 0.08 times the mass of the Sun - at this mass the object cannot fuse hydrogen in their cores, but can fue dueterium (heavy hydrogen). By observing such objects which are thought to have disks around them, Herschel will be able to measure the cold dust present around them. This will aide planet formation theories and our understanding of disks.

Lead Scientist: Paul Harvey (University of Texas at Austin)

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Tracing Remnant Gas in Planet Forming Debris Disk Systems

Previous studies in the infrared and sub-mm have indicated that once stars reach ages of 10-100 million years they have too little gas to form gas giant planets such as Jupiter and Saturn. However, whether there is enough to form ice giants like Uranus and Neptune is uncertain. By looking at emission from oxygen with the PACS instrument, astronomers will observe two nearby stars, one (HR 8799) which is known to have giant planets orbiting it, and another (HD 15115) which is being orbited by a disk showing signs of planet formation. This will allow the detection of gas in quantities as small as 1% the mass of the Earth, and should constrain theories of how these ice giant planets are formed.

Lead Scientist: Vincent Geers (ETH Zurich)

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Guaranteed Time (Round 1)


SPIRE spectroscopy of protoplanetary disks

This project observes the same sources as the "DIGIT" programme but with the SPIRE spectrometer, extending the wavelength range over which they are studied. The sample inclused stars with ages ranging from 1 million to 10 million years, and with masses 1-5 times that of our Sun.  The main purpose is detecting emission lines from atoms and molecules such as carbon, carbon monoxide (CO), water (H2O), silicon oxide (SiO) and ammonia.  The details of the carbon monoxide emission, and in particular the ratios of differen isotypes of carbon in the molecule, will provide powerful constraints on the density and temperature structure of the disk. Water vapour lines will provide further constraints on the density and radiation field in the regions inside the "snow line" of the planetary system, where rocky planets could form.

Lead Scientist: Göran Olofsson (Stockholm Observatory)

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Open Time (Key Programmes)


GASPS: Gas in Protoplanetary Systems

GASPS is the first extensive, systematic survey of gas in circumstellar disks.  The brightest spectral lines from disks lie in the far-infrared and arise from regions where giant planets are expected to form. Herschel is uniquely able to observe this wavelength regime with the sensitivity to allow a large scale survey. Using PACS, this project with observe carbon and oxygen in 274 objects, and look for water in the brightest sources. This will allow the amount of gas in the systems to be measured bettern than previously possible.  We will observe nearby star clusters in the age range 1-30 million years, covering the key period of planet formation, and the observed stars and protoplanetary disks will be of a range of sizes.

Click here to go to the GASPS website.

 Lead Scientist: Bill Dent (UK Astronomy Technology Centre)

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DEBRIS

The main goal of DEBRIS is to detect and characterize dusty debris discs around nearby main sequence stars. The survey targets almost 450 stars in order to understand statistically how many stars harbour debris discs.  It will conduct PACS observations of each target at 100 and 160 microns, sufficient to detect discs with dust content comparable to the Kuiper Belt around the Sun. The brightest objects will also be observed with SPIRE at wavelengths of 250, 350 and 500 microns.  The multi-wavelength data will enable the dust temperature and disk radius to be calculated.

Click here to go to the DEBRIS website.

Lead Scientist: Brenda Matthews (Herzberg Institute of Astrophysics)
UK contact: Jane Greaves (University of St Andrews)

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DUNES: Dust discs around nearby stars

DUNES will use the unique imaging capabilities of Herschel to perform a deep and systematic survey for faint, cold debris disks. The aim is to find analogues to the Kuiper Belt in a sample of 283 nearby stars like the Sun. All the stars are within about 80 lightyears, and have masses from 1/5th to double that of the Sun. This will provide an unprecedented lower limit to the abundance of such systems, and allow astronomers to detect the presence of giant planets similar to Neptune and Jupiter in the solar system. The observations will allow them to characterize, model, and constrain the disks, and as a result, it should be possible to detect systems similar to out own Kuiper Belt.  The extensive and unique data set will address some fundamental questions related to such discs: dependence of planetesimal formation on stellar mass, the evolution of discs over time, the correllation with any planets, and the properties and size of dust grains. Herschel is the first and the only facility for the foreseeable future which is providing the observational capability required to successfully answer these questions, and the outcome of this project will leave a legacy impacting on our knowledge of planet formation and planetary systems.

Click here to go to the DUNES website.

Lead Scientist: Carlos Eiroa (Universidad Autonoma de Madrid)

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DIGIT: Dust, Ice and Gas In Time

Dust, ice, and gas evolve as they move from envelopes of forming stars into circumstellar disks where they can become the main building blocks of planets. Herschel-PACS is uniquely suited to trace this evolution through broadband emission from dust, through specific features of solids which reveal elemental composition and water content, and through spectral bands of the main icy components. Both atomic and molecular spectral lines, in particular from oxygen, water and hydroxyl (OH), will be used to follow the gas, study the interchange between gas and ice, and trace the oxygen budget. The gas and dust spectral features are at the same time excellent probes of macroscopic parameters, such as temperature, UV and X-ray fields, density and thermal structures of envelopes and disks, and dynamical mixing processes. Our sample covers sources with a range in evolutionary state from embedded objects with massive envelopes to weak-line T Tauri stars with dissipating disks, and with a range in luminosity, spectral type, and dust characteristics. Both our high sensitivity PACS full spectral range scans (complemented by Spitzer mid-IR spectral scans) and our targeted, deep gas-phase line measurements will have lasting archival value.

Lead Scientist: Neal Evans (The University of Texas at Austin)

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Open Time (Round 1)


Unveiling the kinematics of the MWC49A's ionized disk and outflow with H-recombination line masers.

MWC349A, the unique H-maser source observed so far, is a massive star with an ionized outflow believed to be generated in its photoevaporating rotating circumstellar disk. We plan to use the unique spectral capabilities provided by HIFI to perform observations of basically all of the H-alpha recombination lines (from H26-alpha to H15-alpha) covered by this instrument. Spectral resolved profiles will reveal essential kinematics inormation of the inner regions of the ionized outflow and the rotating disk. The observed line profile will be compared with the prediction of our non-LTE 3D radiative transfer model to constrain key parameters of the disk-outflow system. From the model's prediction we will stablish if the inner disk is rotating with a Keplerian law, the rotation of the outflow and likely the presence of radial motions (accretion/excretion) in the disk and the location of the lunching point of the outflow. These parameters will help to discriminate between the models proposed for the origin of the outflows and the evolutionary state (pre-main sequence or evolved B[e] stars) of the central star.

Lead Scientist: Alejandro Baez Rubio

Allocated time: 7.2 hours

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Search for a correlation between planets and debris discs around retired A stars

Planet formation leads to two detectable outcomes - planets and debris disks. No correlation between these outcomes has been found for main sequence FGK stars. However, planet formation outcome depends on spectral type. Furthermore, the higher incidence of both planets and debris for A stars makes correlations easier to detect. We propose to test for a debris-planet correlation around A stars, by observing 36 subgiants (retired A stars) with PACS to search for debris disk emission. All of these stars have been searched for planets, and 18 have detections. Our population models, calibrated to main sequence disk evolution statistics, predict that we should detect disks toward 23% of our sample. Comparison of debris incidences in the planet and control samples will quantify any debris-planet correlation, which would provide valuable constraints for planet formation models. Even without such a correlation, we expect to find 4 debris-planet systems, adding to the 10 currently known, which would provide a significant advance in our understanding of the dynamics of planet-disk interactions, and so of how these systems could have formed. Also, since the post-main sequence debris disk population is currently poorly known, any disk discovery (or lack of it) will provide important new constraints on the evolution of debris in this phase.

Lead Scientist: Amy Bonsor

Allocated time: 20.3 hours

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Solving the beta Pictoris carbon puzzle by HIFI observations of CII

The nearby young A-star beta Pictoris is well known for its large circumstellar dust disk. The disk is also known to contain gas, which from absorption lines in the UV is found to be overabundant in carbon by a factor ~20. Recently, Herschel/PACS observed very strong emission from the CII line which seems to indicate that the disk is even more abundant in carbon than previously thought, up to a factor of 100 above other elements. This is unexpected, and we propose to investigate this with HIFI high-resolution spectroscopy of the CII 157um line profile. From the known Keplerian velocity field and the line profile, we will be able to constrain the spatial location of the carbon and thus the total carbon mass. The spatial location of the carbon gas will also give clues to its origin, in particular if it is related to the recently discovered planet in a ~10 AU orbit around beta Pic.

Lead Scientist: Alexis Brandeker

Allocated time: 8.4 hours

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Herschel observations of solar−type stars with planets, planetesimals and dust

Similar to the Solar system, there are only 18 planetary systems known to harbor planets and planetesimals. This small sample is of unique value to our understanding of the diversity, dynamical history, and formation mechanisms of extra-solar planetary systems. Here we propose to observe seven of these systems, with spectral types F7-K2 and ages from 0.5-6.4 Gyr. They all show excess emission at 70 um but not at 24 um, implying the presence of an inner region depleted of warm dust, resembling the Solar System in its Jovian planets + Kuiper belt configuration. It is possible to characterize their planetesimal belts from the study of their dust disks. However, the disks SEDs are not known beyond 70 um. Long wavelength observations are of fundamental importance to determine the presence of cold grains, the only tracer of the outer edge of the dust-producing planetesimal belts. Because the latter is a critical parameter to understand the dynamical history and formation of these systems, we propose to carry out PACS 70/160 and SPIRE observations with the main goal of constraining the SEDs at long wavelengths. We have selected PACS 70 to take full advantage of the Herschel’s improved spatial resolution at 70 um compared to Spitzer, opening the opportunity to resolve the cold dust component that traces the planetesimal belt (which extent could be related to the dynamical history of the planetary system), and to detect extended halos (thought to arise from small dust grains on highly eccentric or hyperbolic orbits, that likely relate to the level of dynamical activity in the planetesimal belt). This proposal requires a total of 11.6 hours. The results will increase our understanding of the diversity of planetary systems, helping us place our Solar system into context. Herschel is the only observatory that can carry out the observation required for this study because of its high sensitivity in the wavelength range where the peak of the dust emission may be located.

Lead Scientist: Amaya Moro-Martin

Allocated time: 11.6 hours

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Dust and gas in brown dwarf disks: A multi-wavelength survey with Herschel

Disks around young brown dwarfs are a valuable test regime for our current understanding of star and planet formation. The disk sizes and masses are key indicators to assess the significance of dynamical encounters for the formation of very low mass objects. The disk mass, together with the properties of the dust, also constrains the potential for planet formation around brown dwarfs, which can be used to evaluate the diversity and ubiquity of planetary systems. To tackle these science goals, we need constraints on the global characteristics of brown dwarf disks. This requires multi-wavelength observations of the far-infrared/submm continuum to trace the distribution and properties of the dust in the disk, as well as line spectroscopy to probe for the presence and amount of gas in the disk. Herschel is uniquely suited for such a project. Here we propose to observe a well-characterised and carefully selected sample of 16 brown dwarfs with PACS and SPIRE photometry, complemented by PACS line spectroscopy for the 3 brightest objects. We expect to provide the first robust assessments of the masses and sizes of disks in the substellar regime. For the first time, we will be able to probe the dust opacity and the amount of gas in the brown dwarf regime, crucial parameters for the understanding of the disk physics. These observations will gain further value in synergy with planned submm interferometry campaigns with SMA and ALMA in the next year. Our project constitutes a significant step towards a solid characterisation of brown dwarf disks.

Lead Scientist: Alexander Scholz

Allocated time: 13.6 hours

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Tracing global protoplanetary disk dispersal and evolution in Cep OB2

We propose to use Herschel PACS photometry observations at 70 and 160 microns to study the global structure of protoplanetary disks in different stages of evolution. Our goal is to determine the contribution of the various physical disk dispersal mechanisms (grain growth/settling, planet formation, photoevaporation) for a uniform sample of disks with different ages and stellar masses. Far-IR observations are extremely sensitive to the global disk properties (flaring, small dust grain depletion, total disk mass). The data will constrain the disk structure as well as the way evolution proceeds (inside-out evolution versus homologous depletion), revealing the effects of the different dispersal mechanisms and their interplay depending on the age and mass of the systems. We will study a large sample of disks in the Cep OB2 region, which contains three populations with ages 1, 4, and 12 Myr. Cep OB2 has been extensively studied at optical and IR(Spitzer) wavelengths, so the properties of these stars and their inner disks (including the presence of gas and accretion)have been determined. Millimeter observations are also available for 32 objects. The sample contains 59 disks (observed with IRS) plus ~120 additional cluster members for which we have optical, IRAC and MIPS data. The disks span a wide range of SED types, from flared, primordial disks with small grains to flattened objects without silicate features and transition objects with cleared or optically thin inner disks, and also show differences in the gas content and accretion. By combining the PACS photometry with our available multiwavelength data and our RADMC radiative transfer code for disk modeling, we will be able to trace the global disk structure/dust content of the objects. We will then examine the global trends of disk structure and evolutionary status within the full sample, checking its dependency of age and stellar mass in order to understand the effect of the different physical processes on disk dispersal.

Lead Scientist: Aurora Sicilia-Aguilar

Allocated time: 23 hours

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Testing Planetary Dynamics and Evolutionary History in the HR 8799 Planet/Disc System

We propose to map the debris disc associated with the multi-planet system HR 8799 in order to constrain the current dynamical state of the planetary system and refine models for dust production in the disc, thereby testing models for the origins of the three known giant planets. Herschel's sensitivity and resolution make it possible to image both the cold planetesimal disc (posited to lie between radii of 90-300 AU) as well as the fainter extended halo (300 - 1000 AU radius) at multiple wavelengths. Direct detection of the edges of the cold belt of dust and an independent measure of the system's inclination will provide critical constraints on models of the planetary orbits within the system, particularly for the outer-most planet for which mass and orbit information can be constrained by simultaneous fits to the planet and disc. The combination of three massive, coeval, and spectroscopically characterizable planets, together with the dust disc, makes this system a "Rosetta Stone" for planet formation studies. The disc is also important for differentiating between planet formation scenarios. Models predict variations in resonance structure for migration versus in situ formation, and multi-wavelength variations in observed structure within Herschel's wavelength range in the case of planetary migration. This proposal is at the very heart of Herschel's top science goal of understanding the mechanisms involved in the formation of stars and planetary bodies. The resolution, sensitivity and multi-wavelength imaging of Herschel are crucial to this program.

Lead Scientist: Brenda Matthews

Allocated time: 9.8 hours

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Disk masses for ~10 Myr old brown dwarf disks

We request SPIRE 200-500mu observations for two brown dwarf disks, 2MASSW J1207334-393254 (2M1207) and SSSPM J1102-3431 (SSSPM 1102), in the TW Hydrae Association (TWA). From our previous Spitzer observations, we had confirmed excess emission at wavelengths of ~5-38mu for both of these sources. With the SPIRE observations, we can probe the optically thin dust in the outer cooler regions of these disks. We have performed radiative transfer modeling for these systems. With the available mid-infrared observations, we find high degeneracies for the disk mass and outer disk radius estimates. Observations at far-infrared wavelengths can help constrain the model fits and obtain better estimates for the disk mass and outer radius for these disks. At an age of ~10 Myr, 2M1207 and SSSPM1102 are the oldest known brown dwarf disks. It is thus important to estimate the disk masses for these older disks, and to understand, in comparison with the younger Taurus systems, if brown dwarf disk masses show any decline with the age of the system. We also request PACS 70mu photometry for another candidate brown dwarf disk in the TWA, 2MASSW J1139511-315921 (2M1139). This object shows an excess emission at 24mu, but none at shorter wavelengths. With 70mu observations, we can confirm if the disk flares up at longer wavelengths. If the presence of such a disk is confirmed for 2M1139, then this would be the first transition disk detected among the sub-stellar members of TWA.

Lead Scientist: Basmah Riaz

Allocated time: 3 hours

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Do stars with rocky terrestrial planets also have Edgeworth-Kuiper Belts?

We propose to measure with PACS the broadband far-infrared spectrum of some young A- and F-type main sequence stars with known, exceptionally luminous, mid-infrared emission. Such stars are uncommon but are of special interest because they point to and delineate the era of rocky terrestrial planet formation. Herschel observations will establish whether cool dusty regions analogous to the Sun's Kuiper Belt region accompany inner regions where terrestrial planet formation is occurring.

Lead Scientist: Ben Zuckerman

Allocated time: 4.9 hours

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A Search for Water Ice in Exo-Kuiper Belts

We propose to obtain PACS full range spectra of 6 bright debris disks (with 70 micron fluxes >0.5 Jy) that have been spatially resolved in scattered light. We plan to search for far-infrared emission features due to water ice and other species. Herschel PACS is expected to be the premier tool for characterizing dust around debris disks because the grains in debris disks are believed to be (1) large (with minimum blow-out sizes great than one a few microns) and (2) cold (with typical grain temperatures less than 70 K). Our proposed sources possess high albedos, suggestive of water ice. A Herschel detection of water ice would be the first definitive detection of water ice in an external Kuiper Belt.

Lead Scientist: Christine Chen

Allocated time: 20 hours

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A Clearer View of Dust Evolution in Protoplanetary Disks

We propose to quantify dust evolution in protoplanetary disks around low-mass pre-main sequence stars, the precursors of our own Sun. To this end, we will measure grain growth and settling, the first two steps towards planet formation, in disks located within the star-forming clouds of Taurus, Chamaeleon, and Ophiuchus. In addition to studying "full" disks we will also target objects which are in the process of clearing gaps in their disks, a phenomena which is most likely due to newly formed planets. By combining spectral energy distributions that employ mid-infrared Spitzer and submillimeter Herschel data with spatial brightness distributions obtained with interferometers in the millimeter (SMA, ALMA), we will provide a self-consistent analysis of the amount of dust growth, settling, and clearing in disks, which will also serve as a guide for future disk studies with JWST. The systematic, semi-empirical evidence obtained through this proposed study will provide needed insight and constraints to aid in theoretical modeling of dust evolution and planet formation, bringing us a few steps closer to understanding the origin of our own solar system.

Lead Scientist: Catherine Espaillat

Allocated time: 30 hours

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Settling an Icy Issue: Using Dust and Ice in Young Disks to Constrain Theoretical Models

We propose to obtain PACS range spectroscopy to measure the amount of water ice and dust evolution in protoplanetary disks located within the ~1-2 Myr old Taurus, Chamaeleon, and Ophiuchus clouds. Theoretical works show that grain growth and dust settling are critical first steps in forming planets and that the ice content of disks plays an influential role in the coagulation process. However, the amount of dust evolution actually experienced by disks and their real ice content is largely unconstrained. To provide a quantitative link between theory and observations we will target 40 disks, many of which show signs of planet formation as inferred from gaps and holes in their dust distribution. We will use irradiated accretion disk models to do a self-consistent analysis of their spectral energy distributions utilizing multi-wavelength data from Spitzer and Herschel. This study will determine the degree of dust evolution experienced by the disks and their ice abundances which can serve as constraints for theoretical models of disk evolution and planet formation.

Lead Scientist: Catherine Espaillat

Allocated time: 20.8 hours

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Exploring the gaseous component of debris disks of high fractional luminosity : a deep [O I] 63.2 micron survey with Herschel.

Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. However, there is a very small interesting group of stars in our neighbourhood (49 Ceti, and our discovery HD 21997), which may represent the missing link between these phases as indicated by the unexpected presence of debris-like dust content and measurable CO gas component. With the aim of discovering and characterizing more of these spectacular objects here we propose to obtain [O I] 63 micron observations of a sample of carefully selected young (<50Myr) debris disks of high fractional luminosity with Herschel/PACS. Our objectives are to 1) discover and determine the incidence of 49 Ceti-like gaseous debris disks; 2) characterize disk structure; 3) determine the timescale of gas dispersal; 4) perform a detailed investigation of HD 21997. New discoveries would lead to the definition of a new subclass of circumstellar disks, the gaseous debris disks. We required 17.2h of Herschel time for the observations.

Lead Scientist: Csaba Kiss

Allocated time: 17.2 hours

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Herschel characterization of the new class of dusty first-ascent giant stars

We have recently discovered a new class of first-ascent giants surrounded by substantial dusty and gaseous disks that are sometimes accreting onto the central star. These old stars, who are nearing the end of their lives, are experiencing a rebirth into characteristics typically associated with newborn stars. As such we dub them ``Phoenix Giants''. As a critical step to understanding these unique systems and the origin of their circumstellar material, we propose Herschel PACS and SPIRE imaging observations to characterize their dusty disks. We expect that Herschel observations of Phoenix Giant disks will establish a benchmark characterization of the outer disk regions of this recently discovered class of first-ascent giant stars.

Lead Scientist: Carl Melis

Allocated time: 13.1 hours

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The neutral disk of MWC349

We wish to study the circumstellar disk of the bright radiostar MWC349 with the aim to infer the evolutionary state of this prominent but enigmatic massive stellar object. We propose to make a full wavelength range scan with PACS and with the SPIRE spectrometer in order to determine the continuum spectrum of the disk, especially in the ill determined or unexplored wavelength region centered on 200-300 microns where the emission from the ionized wind and the warm circumstellar dust are comparably strong. These spectral scans are at least 10x more sensitive than our ISO data, and permit a deep search for molecules like water and CO. The presence of water which is being found by Herschel in a range of accretion disks young stellar objects would be strong evidence for the nature of the MWC349 disk as due to accretion, whereas the absence of water is most easily explained if the disk results from mass loss in a strong stellar wind or ejection event. Our proposed investigation has thus the potential to resolve the half--century old question about the evolutionary state of MWC349.

Lead Scientist: Clements Thum

Allocated time: 5.7 hours

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PACS Photometry of Nearby Warm Debris Disk Systems from the WISE All-Sky Survey

Debris disks trace the collisional breakdown of asteroid and comet parent bodies orbiting nearby main sequence stars. They are detectable in ~16% of FGK stars, nearly twice as often in A stars, and are almost unknown around M stars. The debris disks of sunlike stars are typically cold analogs of our Kuiper belt with emission peaking near 70 microns wavelength. However, a relatively small number of warm disks are known with emission at 24 microns. These systems are especially interesting because they trace dust in the region likely to host terrestrial planets, where the dust has a short dynamical lifetimes. They also tend to be young systems aged < 1 Gyr. This knowledge of warm debris disks - extrasolar analogs to our solar system's Zodiacal cloud - is based on the 25 year old IRAS survey and observations of selected targets with ISO and Spitzer. The Wide-Field Infrared Survey Explorer (WISE) has just completed new, sensitive all-sky mapping in the 3.3, 4.6, 12, and 22 micron bands. Association of the WISE sources to Hipparcos and Tycho stars has led to the identification of 99 nearby main sequence stars with robustly detected warm 22 micron excesses not previously known. To determine whether these systems represent outbursts of asteroidal dust production (such as in the HD 69830 system), or simply the Wien side of emission from a cold outer dust belt, photometry at longer wavelengths is needed. We propose Herschel/PACS 70 and 160 micron photometry of this unbiased sample. These data will allow us to fully characterize the dust temperature and infrared luminosity of these systems, allowing them to be understood in the context of other debris disks and disk evolution theory. The sample includes field M stars as close as 12 pc, the first objects of this class seen to have warm dust emission. The results will strongly constrain our picture of the collisional history of inner planetary systems.

Lead Scientist: Deborah Padgett

Allocated time: 52.8 hours

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A New Method to Determine the Gas Mass in Protoplanetary Disks

The mass of planet-forming disks is one of its most fundanmental quantities and can determine the primary mode of planet formation. Because the dominant constituent, H2, is undetectable, we are forced to adopt indirect methods to trace the total gas content. The primary method used is to observe thermal dust continuum emission at submm/mm wavelengths where the dust emission is optically thin. However, mass estimates are highly uncertain because grain evolution can substantially alter the dust opacity coefficient and the gas-to-dust ratio, which are required to convert total flux to mass. We propose here a dedicated program to use PACS spectroscopy to search for the emission of HD J=1-0 at 112 microns and derive the gas mass from a tracer that uniquely probes H2. HD will co-exist with H2 in the gas phase and is the dominant reservoir of deuterium, carrying the cosmic D atom abundance. Our program is a comprehensive effort where observations will be combined with chemical theory and excitation modeling to enable the conversion of integrated emission to mass. This program offers a unique opportunity to derive disk gas masses via an independent method with important implications for the formation of planetary systems.

Lead Scientist: Edwin Bergin

Allocated time: 21.1 hours

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Debris Disks around Planet-Bearing Stars

The relationship between planets and debris disks is unclear. On one hand the direct imaging of planets in three systems with prominent debris disks (beta Pic, HR 8799, and Fomalhaut) suggests a direct link between the two phenomena. Indeed, the eccentric shape of the Fomalhaut dust ring is clearly driven by its shepherding planet, whose existence and eccentricity were correctly predicted based on the disk asymmetry. On the other hand, Spitzer surveys fail to find any correlation between cold debris at 10's of AUs and radial-velocity-detected planets in the inner system. Motivated by Herschel's advantages over Spitzer, we propose to further explore the planet-debris relationship by observing 67 stars known to have planets. For the 9 targets that are already known to have orbiting debris, we will resolve the disks, determining the location of the dust-producing planetesimals and measuring disk asymmetries that may be induced by neighboring planets. For the remainder of the targets we will search for new debris disks and then look within the overall sample for any correlations with planet properties.

Lead Scientist: Geoffrey Bryden

Allocated time: 67.2 hours

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A Disk Census for New Low-Mass Members of TWA

We propose to conduct a protoplanetary and debris disk survey of 14 recently-identified members of the benchmark (10 Myr) TW Hya Association (TWA). Our new sample expands the member census by tripling of the low-mass population (>M5; <0.2 M_sun). TWA represents a critical age where the longest-lived protoplanetary disks and the youngest debris disks overlap in the same population, so it offers a critical window into the formation and evolution of planetary systems. We specifically propose a PACS 70/160 micron photometric census to identify new disks, and followed by SPIRE 200/250/350 micron photometric observations of all newly-identified disk systems to characterize their SEDs and determine the nature of their circumstellar disks (protoplanetary or debris). Based on the disk fraction among known late-type members (3/6 = 50%), we estimate that 6-7 of our targets are likely to host circumstellar disks; these disks have been incredibly rare until now, so each will be a prime target for future studies of accretion, disk evolution, and planet formation.

Lead Scientist: Greg Herczeg

Allocated time: 9.2 hours

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Using PACS and SPIRE photometry and spectroscopy to characterise the discs of Herbig Be stars: structure, gas content and cold crystalline dust composition.

Herbig Be stars are the link between massive protostars and the intermediate-mass Herbig Ae stars. While for this last group the disc has been characterised in terms of flaring/flat geometries in which dust grains grow and settle towards the midplane, and the bulk of the gas dissipates after 5 Myr, the picture of a disc around a more massive star is less clear. Therefore, we propose to observe a sample of 40 Herbig Be stars, in an effort to determine their disc properties. In particular, we aim at answering the following questions: 1) How do these discs dissipate?, 2) Does grain growth and settling occur? 3) Can gas giant planets still form, and what is the stellar upper mass limit for their formation?, and finally 4) How do the Herbig Be discs differ the lower mass Herbig Ae and T Tauri discs? To answer these questions, we propose to use PACS and SPIRE in photometric mode for the whole sample, and in spectroscopic mode for a subset of the 6 brightest - most promising targets. We will complement the proposed observations with existing optical to mid-IR photometry, as well as mid-IR spectroscopy, to construct spectral energy distributions (SED). These SEDs trace the dust continuum and will be analysed with the aid of radiative transfer modelling. For part of the sample, we also have mid-IR images or interferometry, revealing the spatial extend at those wavelengths. In a next step we will relate the derived disc properties with stellar properties. In addition, for the 6 spectroscopic targets we will be able to make a detailed case study of their cold dust and gas content: the forsterite feature at 69 micron reveals the iron content in the crystalline dust, and gas lines of e.g. OI and CO will allow us to constrain the amount of gas still present in the disc, using both radiative transfer modelling as well as thermo-chemical models. The proposed observations will provide a valuable database for a better understanding of the disc structure and evolution in the more massive Herbig Be type stars.

Lead Scientist: Gwendolyn Meeus

Allocated time: 33.4 hours

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Characterizing the evolved, planet-forming disks orbiting the old classical T Tauri systems V4046 Sgr and MP Mus

V4046 Sgr and MP Mus are the second and the third closest known classical (actively accreting) T Tauri systems, respectively (the intensively studied TW Hya being the closest). We have recently established that, like TW Hya, both systems are orbited by dusty, molecular disks. Given their proximity (d<100 pc), ages (~10 Myr), and masses (0.7-1.2 solar masses), these three systems represent readily-studied analogs of the young sun during the crucial, late phases of the star formation process, when the circumstellar disk still retains a significant gaseous component and giant planets likely are forming or have recently formed. Furthermore, the close binary V4046 Sgr affords an unusual opportunity to investigate planet formation within circumbinary disks. We propose to observe the V4046 Sgr and MP Mus disks using Herschel's PACS and SPIRE spectrometers with the complementary aims of (1) measuring the detailed spectral energy distribution of the continuum dust emission between 55 and 670 micron and (2) detecting the brightest atomic emission lines. These data, together with the comprehensive suite of X-ray, mid-infrared and radio observations we are already collecting for these two systems, will allow us to fully characterize the physical properties of both the dust and the gas components of their circumstellar disks and to investigate the effects of high energy emission from the central star on the evolution of the circumstellar, planet-forming environment.

Lead Scientist: Germano Sacco

Allocated time: 14.4 hours

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Planets, Debris Disks, and the Lambda Bootis Stars

We propose to explore the link between lambda Bootis stars, debris disks, and planetesimal formation and evolution. The lambda Boo stars are a rare type of peculiar A star (2%), which are Population 1 and metal poor. Planet bearing systems and debris disk stars appear unusually well represented in the lambda Boo class: for example, beta Pic, Vega, and HR 8799 are all lambda Boo candidates. A small sample of 14 lambda Boo stars observed by Spitzer suggests an occurrence of infrared excess approaching 100%. Only two lambda Boo stars are included in the DEBRIS/DUNES Herschel key program debris disk surveys. We will use PACS/Herschel to make sensitive, high-resolution maps of 27 new lambda Boo stars. Like DEBRIS/DUNES, we will reach the stellar photosphere for all targets, enabling a measurement of the true rate of excess infrared emission among lambda Boo stars compared to normal A stars. The depletion pattern of heavy elements in the atmospheres of lambda Boo stars suggests they may have accreted gas from which dust grains have condensed and been removed: this gas may be circumstellar gas that has formed planetesimals or dusty interstellar gas. While the circumstellar disk scenario predicts sizes of a few hundred AU, the cloud accretion scenario predicts 1000-2000 AU bow structures oriented in the direction of the relative motion of the cloud and star. With target distances of < 140 pc, these bow structures are expected to be resolved for all targets. These will be the first mid-infrared observations of lambda Boo stars outside of the low density Local Bubble: if interstellar medium interactions dominate the lambda Boo phenomenon then systematic variations in excess strength and morphology may occur with distance.

Lead Scientist: Holly Maness

Allocated time: 7.1 hours

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Taming the Invisible Monster: The Disk of Epsilon Aurigae in the Far-Infrared

We propose to obtain photometric flux density measurements of the remarkable binary star Epsilon Aurigae in all six of the PACS and SPIRE imaging bands. Epsilon Aur is seen close to edge on, and has long (2 yr) eclipses every 27.1 yr. The last eclipse, during 1982-1984, received world-wide attention from astronomers. During 2009-2011, the system is again in eclipse and is the focus of a world-wide observing campaign enlisting both professional and amateur astronomers. Epsilon Aur consists of a high luminosity post-AGB F0 star with a much less luminous stellar companion. The latter is newly proven by us to be surrounded by a solar system-sized disk of cool dust. This disk is a rare example of an evolved disk, composed of the remnants of the endgame of stellar evolution, rather than a "primordial" disk as found in T Tauri stars and A stars like Beta Pic. Gaps in the Epsilon Aur disk, reminiscent of the structure of the rings of Saturn, were recently inferred from ground-based time-series spectroscopic observations. By analogy to the role of shepherd moons in the rings of Saturn, this suggests that there could be planetesimals, dwarf planets, or even full-size terrestrial planets in the Epsilon Aur disk. The spectral energy distribution of Epsilon Aur is well-sampled from the far-UV to the mid-IR (0.1-70 microns), with one radio measurement at 1200 microns. However, it is currently unconstrained in the wavelength region spanned by PACS and SPIRE, which is dominated by the dust disk. These Herschel instruments are uniquely configured to provide high S/N photometry bridging the gaps between the mid-IR and radio regimes. These SED points are crucial to confirm if a non-blackbody slope is present, relating to dust grain emissivity, and if potentially bright emission features from molecular species might dominate. These observations will contribute to understanding stellar evolution in binary stars, as well as the formation, evolution, and rejuvenation of planetary systems.

Lead Scientist: D. W. Hoard

Allocated time: 3.6 hours

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Understanding the Origin of Transition Disks via Disk Mass Measurements

Transition disks are a distinguished group of few Myr-old systems caught in the phase of dispersing their inner dust disk. Three different processes have been proposed to explain this inside-out clearing: grain growth, photoevaporation driven by the central star, and dynamical clearing by a forming giant planet. Which of these processes lead to a transition disk? Distinguishing between them requires the combined knowledge of stellar accretion rates and disk masses. We propose here to use 43.8 hours of PACS spectroscopy to detect the [OI] 63 micron emission line from a sample of 21 well-known transition disks with measured mass accretion rates. We will use this line, in combination with ancillary CO millimeter lines, to measure their gas disk mass. Because gas dominates the mass of protoplanetary disks our approach and choice of lines will enable us to trace the bulk of the disk mass that resides beyond tens of AU from young stars. Our program will quadruple the number of transition disks currently observed with Herschel in this setting and for which disk masses can be measured. We will then place the transition and the ~100 classical/non-transition disks of similar age (from the Herschel KP "Gas in Protoplanetary Systems") in the mass accretion rate-disk mass diagram with two main goals: 1) reveal which gaps have been created by grain growth, photoevaporation, or giant planet formation and 2) from the statistics, determine the main disk dispersal mechanism leading to a transition disk.

Lead Scientist: Ilaria Pascucci

Allocated time: 43.8 hours

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Close Binaries with Infrared Excess: Destroyers of Worlds?

We have recently used Spitzer to confirm that large IR excesses seen in about 20-30% of old close binary stars by IRAS correspond to very warm close-in dust that appears to originate from recent collisions of planets or planetesimals (Matranga et al. 2010). Somehow, close binaries seem to be destabilizing their planetary progeny, perhaps through secular shrinkage of the stellar separation caused by magnetically-driven angular momentum loss. The aim of this proposal is to use Herschel to search for excesses characteristic of Kuiper-belt-like cold dust or planetesimals in a sample of 88 close binaries from an approved Spitzer IRAC survey. Probing these larger radii in such systems will provide a robust sample of broad SEDs to understand debris disks in close binaries, provide insight into the possibly origin of the Earth mass or more of dust required, and give us a unique handle in understanding planetary formation in circumbinary disks.

Lead Scientist: Jeremy Drake

Allocated time: 16.4 hours

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Very Large Debris Disks from the PLANCK submillimeter All-Sky Survey

Debris disks are analogs of our Kuiper Belt in the periphery of the Solar System, but are surrounding other main sequence stars. Comets in the Kuiper Belt, and more generally planetesimals in a debris disk, are left over from the early phase of planet formation according to the ''core-accretion" theory and are connected to a planetary system orbiting closer in. Differently, an alternative theory for the formation of giant planets distant from their star invokes ''gravitational instabilities'' in young, large, and massive protoplanetary disks, and predicts no left over planetesimal in a peripheral disk at the end this fast process. Hence, existence and sizes of debris disks are a central question in planet formation theory. The PLANCK in-orbit observatory is conducting the first all-sky survey in the submillimeter and offers the first opportunity for an unbiased survey of very large, and cold debris disks. We have used the existing PLANCK data to identify debris disk candidates spatially unresolved with the PLANCK beam (4.2'). We propose to confirm their nature by spatially resolving them with the Herschel SPIRE camera, and to determine their sizes by imaging and dust temperature by sampling their SED at 250, 350 and 500um. If successful, we would have identified a new population of very large, and cold debris disks characterized by distant planetesimals from their central star, supporting the ''core-accretion'' theory for giant planet formation.

Lead Scientist: Jean-Francois Lestrade

Allocated time: 5.6 hours

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How to produce warm dust around warm debris disks? - Testing the outer Planetesimal Belt Scenario

During the last decade, some peculiar objects emerged from mid-infrared observation campaigns: warm debris disks. These unique and rare objects have the same properties as "classical" debris disks, except that they display emission features in the mid-infrared, that are associated with warm micron-sized silicate grains. The origin of the warm dust component is still subject to discussion. According to the most recent studies, this dust population may be the consequence of two scenarios. The first explanation would be that a recent catastrophic collision took place in the inner regions of the disks, producing a large amount of micron-sized grains. The second possibility is that a cold outer planetesimal belt is feeding the inner regions, in a similar way as the Late Heavy Bombardment that took place in the Solar System. Such dynamical instability can possibly be triggered by giant planet's migration. We propose to use the PACS photometer, combined with SED modeling, for a unique set of 6 warm debris disks, than may host on-going planetary formation, in order to search for emission in excess at long wavelengths, that may reveal the presence of outer planetesimal belts.

Lead Scientist: Johan Olofsson

Allocated time: 7.3 hours

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Polycyclic aromatic hydrocarbons (PAHs) in protoplanetary disks around late-type T Tau stars in Orion Nebular Cluster

We propose a search for far-infrared features from polycyclic aromatic hydrocarbon molecules (PAHs) in a small sample of protoplanetary disks around late-type T Tau stars. These objects were identified in the course of our large Spitzer-IRS survey of the Orion A cloud to have mid-infrared PAH features with unusual profiles, which are far too bright to explain by photoexcitation by their host stars; they must be excited by ultraviolet light from their more massive neighbors. Recent laboratory spectra of PAHs demonstrate the variation of wavelength and strength with molecule size for the far-infrared features of PAHs, a sensitivity that is lacking in the mid-infrared features. The observation of such features in disks around low-mass stars, in which we frequently see the effects of coagulation and growth among the silicate-grain population, represents an opportunity to search for size variation among the PAH population, a congruence with the PAH molecules found in the primitive meteorites, and perhaps hints of the role played by carbonaceous molecules in the assembly of solid bodies in disks.

Lead Scientist: Kyoung Hee Kim

Allocated time: 31.3 hours

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Cool Herschel/Hot Spitzer: The distribution of water in protoplanetary disks

One of the key mission objectives of Herschel is to observe water in various environments, but in protoplanetary disks in particular. Water has an immediate relevance to the formation of planets and to our own origin. We propose to obtain deep PACS/SPIRE line spectra of water, OH and CO in protoplanetary disks already known to have strong rotational water vapor emission at mid-infrared (10-36 micron) wavelengths, as detected by Spitzer (the newly discovered mid-infrared molecular forest). The mid-infrared lines trace warm to hot gas formed within a few AU from the central star. The proposed observations will relate the oxygen chemistry and transport of water in the inner few AU with that of the cooler outer disk - 1-100 AU - as traced by the PACS water lines. The line ratios of water in the Spitzer spectral range suggest that water vapor may be strongly depleted in the disk surface beyond 1 AU although gas and dust temperatures are high enough to maintain abundant water out to at least 10 AU. It was suggested by Meijerink et al. 2009 that this depletion of water could be due to a ``cold finger effect'', in which the surface water vapor is carried downwards into colder regions of the disk where it freezes out and is bound in the disk mid-plane as part of the general dust growth and settling. If so, the surface abundance structure of water is a direct tracer of the mid-plane snow-line. Based on model fits to the mid-infrared lines, we predict very strong differences in the 50-200 micron water lines, depending on the distribution of water in the outer disk surface. Our program is unique in that 1) we specifically target disks known to have strong water emission from the inner disk and 2) we go significantly deeper than others ensuring that we can constrain the abundance of water vapor down to 10^-10 per hydrogen in the outer disk, thus putting very strong constraints of the efficacy of the proposed cold finger effect.

Lead Scientist: Klaus Pontoppidan

Allocated time: 39 hours

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Dusty Disks around Hot White Dwarfs: Debris Disks or Remnant of post-AGB Binary Disks?

Dusty disks around hot (Teff > 100,000 K) white dwarfs are a new phenomenon discovered by Spitzer. The origin of such a disk is still in debate. We propose to obtain far-infrared photometry for 6 dusty disks around hot WDs identified from our Spitzer 24 micron survey. The Herschel far-infrared measurements will provide strong constraints on the outer boundary of the disk and its total dust mass in the system, crucial information necessary to differentiate the origin of the disks.

Lead Scientist: Kate Su

Allocated time: 7.6 hours

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Deep HIFI searches for cold water vapor in protoplanetary disks

Water vapor inside planet-forming disks is expected to show large variations. In the warm (~200 K) inner few AU of the disk all oxygen is locked up in water vapor. In the colder outer region water quickly freezes out onto dust grains. However, efficient photodesorption by stellar ultraviolet radiation will return an appreciable fraction back into the gas phase in the upper disk layers. This coupled water ice/vapor system explains the Spitzer observations of warm water in several disks, and predicts the presence of cold water vapor in the outer disk. Through the `Water in Star Forming Regions' (WISH) Key Program, we have recently clearly detected the groundstate line of cold water vapor to TW Hya and very tentatively detected it to DM Tau. Both lines are factors 10-50 weaker than expected. We hypothesize that up to 99% of icy grains have settled to the disk's midplane thus `freeze drying' the upper disk layers. The WISH data do not go deep enough to probe cold water vapor content now that we know that the outer disk is freeze-dried. The only clear detection is TW Hya, which has a distance of only 51 pc. At more typical distances of 100-140 pc, line strengths are lower by factors 5-8, beyond the sensitivity of WISH. We propose much deeper HIFI observations of the H2O 110-101 line at 557 GHz of four targets: DM Tau (to confirm or reject WISH's `very tentative' detection), and HD100546, HD163296, and AA Tau. These disks are, after TW Hya, the closest and largest disks that offer the best chances of detection. Because of the sensitivity of H2O 110-101 to cold water vapor in the outer disk, our observations probe as-of-yet unexplored grain settling in the outer disk and enrichment of the midplane with icy grains. This can boost planet formation, since icy grains coagulate more easily. Our proposal also contains a small request for velocity-resolved CO 10-9 observations with HIFI to study warm (~200 K) gas in these four disks, and investigate if preferential settling of icy grains also affects CO.

Lead Scientist: Michiel Hogerheijde

Allocated time: 46.8 hours

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A Search for Cold Dust Orbiting GD 362, a Highly Polluted White Dwarf With Detected Warm Dust

We propose to observe GD 362 to measure the amount of cold dust orbiting this white dwarf which is already known to possess warm dust. There are two models to account for the large amount of atmospheric hydrogen in this externally-polluted star whose atmosphere is largely helium. (1) The star is accreting from a single Mars-mass parent body. In this case there is no reason to expect cold dust. (2) The star is accreting from an ensemble of 100's of Ceres-mass asteroids; a large amount of cold dust likely is present. If so, the source could be detected with PACS.

Lead Scientist: Michael Jura

Allocated time: 1.1 hours

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Crystal clear: revealing midplane dynamics of protoplanetary disks through the spatial distribution of crystalline dust

We propose to obtain PACS range spectroscopy to measure the vertical and radial distribution of crystalline silicates in 22 protoplanetary disks around pre-main sequence stars. Dynamical processes, such as nebular shocks and meridional flows, are predicted to generate crystals within the warm, inner-most parts of these disks and transport them further out into the planet-forming regions. Therefore the spatial distribution of crystals, which have broad, mid-infrared spectral features, can be used to trace such mechanisms. Since these processes influence core-building and migration, determining their scope is paramount to our understanding of planet-formation as a whole. Recent studies using Spitzer Space Telescope IRS spectra suggest crystals are distributed farther out in protoplanetary disks than can be accounted for by current theories. Over the Herschel PACS 51-73 micron range, the continuum is extremely sensitive to changes in crystallinity as a function of radius, while the dust emission features over this range and the continuum from 102-146 micron are sensitive to changes in crystallinity in the vertical direction. By using irradiated accretion disk models to do a self-consistent analysis of the combined PACS and Spitzer IRS spectra of our 22 targets, we will unveil the midplanes of these disks and trace the influence of inner disk dynamics on the planet-forming region.

Lead Scientist: Melissa McClure

Allocated time: 28.7 hours

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Confirming a sample of luminous debris disk candidates identified in the Herschel ATLAS

Debris disks are the remains of planetary system formation, tracing the existence of planetesimal-sized objects in orbit around main sequence stars. Current and planned surveys of debris disks (including the Herschel Key Projects DEBRIS and DUNES) are deep surveys aimed at characterising the typical population of disks and targeted at samples of a few hundred nearby objects. These deep narrow surveys are relatively insensitive to the rarities in the debris disk population, some of which may be luminous and/or massive disks that have undergone recent disruptive collisional events. We have recently shown that the primarily extragalactic Key Project, the Herschel-ATLAS, can be used as a wide and shallow survey of debris disks by combining its excellent optical coverage and statistical techniques more commonly employed to identify galaxies. The combination of Herschel-ATLAS, DEBRIS and DUNES thus forms a powerful nested tier of surveys that will be sensitive to disks across the spectrum from exosolar analogues to rare disks that cannot be inferred from local populations. In this proposal we seek time to image the three candidate disks that we discovered in the Herschel-ATLAS Science Demonstration Phase with PACS so that we may confirm them as true debris disks and model their SEDs to extract mass, temperature and fractional luminosity. We will confirm whether these disk candidates are in fact the most luminous disks yet detected.

Lead Scientist: Mark Thompson

Allocated time: 1.4 hours

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Herschel spectroscopic study of the extraordinary disk Gomez's Hamburger

"Gomez's Hamburger" (GoHam) is a gas rich protoplanetary disk around a pre-main-sequence A star. Recent observations at infrared and millimeter wavelengths have reveal the extraordinary nature of this source: it is seen almost perfectly edge-on, it is massive and therefore intense in the infrared and millimeter: offering the possibility to detect key species (e.g. H2O, High J CO lines), it is large enough to be spatially resolved at most wavelengths, and it is likely in the process of forming planets. Overall, it appears that GoHam is a key object to study the mechanisms that lead to planetary formation, and it has been left behind in the guaranteed time. Here, we propose to observe this object with the three instrument onboard Herschel to complete the data set we have already gathered for this source. The team, composed of experts in molecular astrophysics, disks, radiative transfer, chemistry, and dust properties, will then make best use of these observations to probe the gas temperature, density, velocity and the dust size distribution as a function of the radial and vertical dimension of the disk. Such results are needed, in the end, to constrain the hydrodynamical models of planetary formation, and chemical models explaining the formation of complex molecules. The total requested time for this program is 10 hours.

Lead Scientist: Olivier Berne

Allocated time: 10 hours

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Spatially resolved far-infrared imaging of bright debris disks: studying the disk structure and the stirring mechanism.

A significant fraction of main-sequence stars are encircled by dusty debris disks. The short lived dust particles of these disks are believed to be replenished through destructive collisions between unseen planetesimals whose orbits are stirred up by some mechanism. In the literature three candidate mechanisms compete: the most commonly invoked self-stirring, the giant planet induced planetary stirring and close stellar flyby. Here we propose to study 10 carefully selected debris disks with Herschel/PACS and Herschel/SPIRE, where young age and a rough estimate of disk size from Spitzer observations hint for stirring mechanisms other than self-stirring. With the new observations we will resolve the debris disks at 70 micron (and in some cases at 100/160 micron as well) and will analyze in detail their structure and to identify stirring mechanism. In our programme we aim to 1) resolve the dust disks and characterize their spectral energy distributions; 2) to study the radial and azimuthal distributions of the cold debris; 3) to identify the stirring mechanism in the disks; 4) to perform a detailed investigation of HR 8799 a star with three large outer planets. The proposed observations will contribute to a deeper understanding of the stirring mechanisms by utilizing the superior spatial resolution of Herschel. The total requested time is 14.8 hours.

Lead Scientist: Peter Abraham

Allocated time: 14.8 hours

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A deep 70 micrometer study of cold circumstellar disks in rho Oph: down below the brown dwarf limit

Most stars form in clusters, and the nearest example of an embedded young cluster is the one in the L1688 cloud of the rho Ophiuchi region. It is one of the best explored star-forming region, an intermediate exemplar between the sparse regions of Taurus and the rich, massive cluster of Orion. With the aim of detecting brown dwarfs (BDs) with masses down to a few Jupiter masses, our group conducted a major preparatory observational project in L1688, where we have spectroscopically confirmed 28 new brown dwarfs. The new discoveries increased the known population of BDs by a factor of 3 and provided the so far most complete census of the (sub)stellar population of the rho Oph cluster. Here we propose a comprehensive study of the cold circumstellar disks of the pre-main sequence population, with particular emphasis on the very low mass objects and BDs. Utilizing the unprecedented far-infrared sensitivity and spatial resolution of Herschel, we will obtain deep 70 and 160 micrometer maps of a 1.6 deg^2 area centred on the L1688 cloud, covering also the location of the 28 new brown dwarfs. We intend to (1) study the most complete population of brown dwarf disks in rho Oph; (2) analyse disk properties and evolution across the stellar mass range; and (3) characterize the protostar population and its luminosity function. Our programme provides the opportunity to characterize the complete, homogeneous population of disks around both young BDs and low-mass stars in "the benchmark protocluster" of rho Oph. The produced deep 70 micrometer map of the region will also have a very high legacy value, since flux densities for sources to be discovered (e.g. new confirmed BDs) can be extracted in the future. The total Herschel observing time for the proposed programme is 12.8 h.

Lead Scientist: Peter Abraham

Allocated time: 12.8 hours

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Conditions for Giant Planet Formation: a Herschel Study of Raw Materials in Selected Debris Disks

Due to the observational difficulties of spatially resolving protostellar disk midplanes near the ice line, where most giant planet formation is thought to take place, most constraints on the possible locations and methods of giant planet formation have come from theory. We propose to use Herschel PACS and SPIRE photometry, and PACS spectroscopy, to observe five debris disks around Solar-type stars, in order to (1) observe young systems where giant planets cannot form, and (2) identify the available raw materials for typical planet formation. We will constrain the range of dust temperatures, and search for crystalline forsterite grains, as well as indirect diagnostics of ice and refractory carbon through deep line scans for [C II] (158 microns) and [O I] 63.2 microns.

Lead Scientist: Sarah Dodson-Robinson

Allocated time: 26.5 hours

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PACS Imaging of the CepOB3b Cluster: Observing the Truncation of Disks in a Rich Young Cluster

We propose deep PACS 70 and 160 micron imaging of the Cep OB3b cluster. After the Orion Nebula Cluster (ONC), Cep OB3b cluster is the 2nd nearest, large (2000 member), young (3-5 Myr) cluster to the Sun. It is older and more evolved than the ONC, making it a superb laboratory for studying the evolution of disks in the cluster environment. The cluster contains two distinct, coeval sub-clusters. Spitzer observations show a lower disk fraction in the sub-cluster containing an O7 star, suggesting that disks are being photoevaporated and destroyed by the UV radiation from the O star. The proposed PACS observations, coupled with near-IR and mid-IR photometry, will measure the truncation of the remaining disks by UV radiation. With these data, we will probe the truncation and alteration of disks in an environment which is likely to be similar to that experienced by the young Solar Sytem.

Lead Scientist: Tom Megeath

Allocated time: 8.3 hours

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Tracing Remnant Gas in Planet Forming Debris Disks : Confronting Theories of Ice-Giant Planet Formation

Recent studies of gas emission lines with Spitzer and sub-millimeter telescopes have shown that 10-100 Myr old stars with debris disks have too little gas left to form Jupiter like gas giant planets. Whether enough gas remains in these systems to form ice giant planets is still unanswered. The [OI] emission line at 63 micron is the most sensitive tracer of gas in the ice-giant region of 10-50 AU in disks, and Herschel PACS is therefore uniquely suited to test theories of ice-giant planet formation. We propose to obtain PACS line spectroscopy of [OI] (63 micron) for a carefully selected sample of four young stars from the FEPS Spitzer Legacy Science Program with ages from 10 to 100 Myr. These extremely well systems harbour prominent debris disks that could be in the process of forming ice giants such as Neptune and Uranus. The proposed observations will probe down to gas masses of 0.3-4 Earth masses, and allow us to constrain prospects for ice giant formation, measure gas-to-dust ratios of 1-10 in evolved disks to compare with planet formation / disk evolution models, and put constraints on whether the dust dynamics in these systems is driven by the remnant gas or by the radiation.

Lead Scientist: Vincent Geers

Allocated time: 4.9 hours

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The chemistry of CH+ in disks around HerbigAe stars

Chemistry of protoplanetary disks have focused on the inner (R<5AU) or outer disk (R>100 AU) but not in the 5-30 AU region where giant planets are formed. The hot organic chemistry of 5-30 AU region can be explored with Herschel. We tentatively detected CH+ emission in four disks at 72.14 micron. CH+ is a starting ion in the reaction network leading to methane, HCN, of C2H2. Two of the disks are known to have an inner gap up to ~10AU. We propose to obtain deep observations of three rotational transitions of CH+ with Herschel-PACS. The aims of the proposals are: 1) confirm the detections, 2) study the excitation condistions of CH+ in disks, 3) explore the hot carbon chemistry in disks with our chemical code, 4) understand the role of inner gap in the disk chemistry.

Lead Scientist: Wing-Fai Thi

Allocated time: 1.5 hours

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Herschel Imaging of the remnant of a hot disk that is gone.

The millisecond pulsar (MSP) binary J102347.67+003841.2 is unique since it once contained an accretion disk around 2001, indicating that it is the first such binary found at the end of its transition from a low-mass X-ray binary to a radio MSP. The accretion disk was likely disrupted by the pulsar wind from the MSP. Using Spitzer, we have found mid-infrared excess emission in the source, probably arising from the remnant of the previous accretion disk. Here we request Herschel/PACS imaging of the binary, seeking to detect the source at 70 and 160 microns. The detection will help establish the general properties of the putative remnant, which is part of our effort to fully study this rare MSP binary system.

Lead Scientist: Zhongxiang Wang

Allocated time: 1 hours

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Open Time (Round 2)


Observing Young Debris Disks with SPIRE

The process by which planets accrete and grow are not fully understood. A unique insight could be provided by measuring the size distribution of the collision products in young systems, as it would constrain their dynamical state and the composition of their planetesimal bodies. We propose to observe twelve systems with SPIRE, determining the particle size distribution slope from their long wavelength photometry, breaking the size distribution/distance degeneracy in their SED models by combining our new data with existing Spitzer and IRAS photometry and determining the geometry of the systems.

The thermal signature of planetary debris disks typically originates from particles up to a thousand microns in size and it typically takes on the order of twenty to thirty million years for particles of that size to reach collisional equilibrium in warm disks and 100 to 200 Myr in cold disks. The distribution of dust in the earliest stages of evolution should be more reflective of the collisional fragmentation function and the effects of aggregation between the smallest particles than the collisional cascade equilibrium distribution function, which is reached at a later stage. The slope of the SED in the Rayleigh-Jean regime is in direct relation to the slope of the particle size distribution. While the particle size distribution in older disks can be approximated via models, it is completely unknown for young systems. With SPIRE we will be able to directly observe the particle size distribution in the earliest stages of debris disk formation, which will then shed light on the nature of planetesimal bodies and their formation!

Lead Scientist: Andras Gaspar

Allocated time: 2.2 hours

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The origin of gas in the two oldest newly discovered gaseous debris disks.

Many young main-sequence stars are surrounded by dusty debris disks, but only very few of them have a detectable gas component. In our APEX survey we discovered two new debris disks containing a substantial amount of molecular CO gas. One of them, the 30 million-year-old HD 21997, is the oldest known gaseous debris disk, making it the best candidate for containing CO gas of secondary origin, produced by sublimation of planetesimals, photodesorption from dust grains, or vaporization of colliding dust particles. We suggest that our discoveries together with the already known objects beta Pic and 49 Ceti form a distinguished group of debris systems that may represent the first stage of gas evolution after the primordial phase. Here we propose new Herschel observations to deduce the physical properties and the origin of gas in our targets, and study the possible physical processes of gas production in the secondary origin scenario. Our immediate objectives are the following: 1) Detection of [O I] 63um and [C II] 158um lines in our targets; 2) physical characterization of the gas/dust disk components; 3) establish the origin of gas and 4) comparison with beta Pic and 49 Ceti, and studying evolutionary aspects. The observation of atomic emission lines in such disks will provide a valuable information on the composition of the released gas and thus on similarity of the volatile composition of Solar System comets to exosolar planetesimals, potentially playing key role in the delivery of volatiles to exoplanets. The study request 9.2h observing time.

Lead Scientist: Attila Moor

Allocated time: 9.2 hours

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A census of debris disks in nearby young moving groups with Herschel.

Nearly all young stars harbour circumstellar disks, that serve as the reservoir for mass accretion onto the star, and later become the birthplace of planetary systems. After the disappearance of the gas component from the disk a dusty debris disk is formed that is believed to mark the location of the planetesimal belt as well. For outlining the evolution of such debris disks traditionally open clusters and field stars were studied, however we argue that the recently discovered young moving groups are more suitable objects for such analyses, due to their proximity and good coverage of the first 50 Myr period of the planetary system evolution. In this proposal we request 70/160 um Herschel/PACS photometric observations for so-far unobserved moving group members. These observations will provide a complete coverage of all known members within 80 pc of five nearby young moving groups (beta Pic Moving Group, Tucana-Horologium, Carina, Columba, and Argus), in the A to K spectral range. Based on the new observations we will identify new debris disks, characterize the disk population within individual moving groups, and study disk evolution by comparing the groups of different ages. The results will be used to verify predictions of the self-stirring model of the evolution of planetesimal disks. We will also compare the properties of debris disks in groups of the same age, looking for additional 'environmental' parameters that affect disk structure over a whole moving group. Our study will be a significant contribution to the census of debris disks in young moving groups, increasing the number of observed sources by a factor of 1.5. Since Spitzer could perform only a limited census and the so-far approved Herschel programs added very few additional moving group obervations, our programme is expected to have a high legacy value.

Lead Scientist: Attila Moor

Allocated time: 28.7 hours

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Ultra-Cold Material in Young Debris Disks

Disks of gas and dust around young stars evolve from massive, gas-rich protoplanetary disks to tenuous disks mainly of dust. These dusty disks, now called debris disks, are produced by colliding and evaporating planetesimals, young analogs of Solar System asteroids and comets. They are intermediate between dense protoplanetary disks and mature extrasolar planetary systems.

Herschel disk surveys have found a number of systems with exceptionally cold debris dust, which is likely a sign of planetesimal belts at surprisingly large distances from the central stars (> 50 AU for a solar-type star) and/or peculiar dust properties. These systems will provide key tests of theories for debris disk evolution and planet formation. However, observations at longer wavelengths are urgently needed to 1) truly measure the dust abundances and temperatures, 2) find any dust components at even colder temperatures, and 3) permit accurate modeling of the dust properties and spatial distributions.

Therefore, we propose confusion-limited SPIRE photometry at 250, 350, and 500 microns for 24 debris disks in nearby young associations, to populate an important region of their spectral energy distributions. The targets are located in the TW Hydra Association, the Upper Scorpius Association, the Beta Pictoris Moving Group, and the Tucana-Horologium Association, spanning a crucial age range for debris disk evolution (10 to 30 Myr). The proposed observations, which are uniquely sensitive to ultra-cold dust, require a total of 3.2 hours. Our targets have all been observed with PACS but not with SPIRE. This proposal is independent (stand-alone) in its goals and execution: in short, we are looking for ultra-cold dust in a sample of young debris disks. However, the final dataset will also increase the legacy value of several other Key Programme datasets.

Lead Scientist: Aki Roberge

Allocated time: 3.2 hours

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A Study of Cold Disks around M dwarfs and the Formation of Extrasolar Planets

M dwarfs are the most populous stars in our local universe, and yet we know little about how they form and how often they form planetary systems. Due to smaller stellar radii, larger gravitational reflex motions, and closer habitable zones, M dwarfs are ideal targets for detecting the first terrestrial mass planets in the habitable zone and will be high priority targets for years to come. Therefore, studying the population and physical characteristics of circumstellar disks around M dwarfs will provide insights into this unique environment in which we hope to find habitable planets. Here, we propose to use the Herschel telescope to collect far-infrared (100 & 160 micron) photometry of a sample of 32 M dwarfs. Our sample represents the best candidates to contain detectable debris disks based on youth and proximity to Earth. Our science goals will be to characterize the physical properties of these disks such as temperature, extent and composition thereby gaining a deeper understanding of the formation and evolution of the planetary systems around low-mass stars. This will also identify the best targets for terrestrial planet search programs based on recent Kepler findings.

Lead Scientist: Angelle Tanner

Allocated time: 27.1 hours

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Studying the collisional processes in the debris disk of Beta Pictoris

Beta Pictoris is a young (12 Myr) main-sequence star surrounded by at least one planet at a distance of ~10 AU, and a dusty debris disk created by catastrophic collisions of planetesimals. We propose to make a deep observation of the 69 micron band of crystalline olivine in the debris disk of Beta Pictoris. The debris disk is resolved with HERSCHEL-PACS. This will enable us to study the collisional processes within the debris disk. The discovery of more than 600 exo-planets in the past two decades has shown an amazing diversity in the properties of planetary systems. The origin of this diversity and the way the solar system fits in must be understood by studying young systems in which planet formation is ongoing, and by comparing the properties of these young systems with the historic records of the formation of the solar system as recorded in e.g. asteroids and comets. Beta Pictoris is a unique object for this, since it is bright and it still shows spectral features since it is young enough to still have small grains. Previous studies have already shown that the crystalline olivine material in Beta Pictoris is very similar to that in our own Solar System. Using the integral-field-spectrometer PACS we will be able to look at the 69 micron band of crystalline olivine at the position where the material is created and further out in the disk. This enables us to follow the complete dust creation, avalanche and blow out processes in the disk. Understanding these collisional processes is very important since they strongly effect the properties, formation and evolution of planetary systems.

Lead Scientist: Ben de Vries

Allocated time: 16.4 hours

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Brown Dwraf Disc Fraction at Ages of ~30-50 Myr

We propose to determine the brown dwarf disc fraction at ages of ~30-50 Myr. A comparison of the disc frequencies for stars and brown dwarfs shows very different trends with age. For the solar-type stars, optically thick primordial discs are virtually non-existent by an age of ~10 Myr. At ages >10 Myr, the inner disc material is significantly dissipated, and the discs have made a transition to the debris phase. In comparison, brown dwarf discs at ~10 Myr exhibit strong excess emission in the Spitzer/IRS 5-35µm spectrum, and also show strong excesses at Spitzer 70µm. The mid-infrared colors for these ~10 Myr old discs are found to be similar to the young optically thick discs in the ∼3 Myr old σ Orionis cluster, which indicates that these are still in their primordial phase. Thus no clear transition from a primordial to a debris phase is observed for the brown dwarf discs even at ∼10 Myr ages, unlike the higher mass stars. Furthermore, we find an increase in the brown dwarf disc frequency by a factor of ~2 between 5 and 10 Myr. We propose to observe with Herschel/PACS a sample of all spectroscopically confirmed brown dwarfs in clusters at ages of ∼30-50 Myr. At present, PACS is the only instrument with the required high sensitivities to observe brown dwarf discs at these ages. Obtaining data for brown dwarfs at ages older than 10 Myr will be important to map the evolution of brown dwarf discs over a wider age range, and to determine if the brown dwarf disc decay time scale is longer than that observed for the earlier-type stars.

Lead Scientist: Basmah Riaz

Allocated time: 19.4 hours

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Herschel Characterization of Dusty Debris Disks

We propose to measure with PACS and SPIRE the broadband fluxes of two partially overlapping classes of nearby main sequence stars. Each star possesses one or both of the following characteristics: (a) it is a member of a known nearby, young, moving group, and (b) it is known to have orbiting cool dust, but the dust has been seen at only one wavelength in the far-infrared -- either with IRAS at 60 microns or with Spitzer/MIPS at 70 microns – or only in the mid-IR with MIPS at 24 microns or with Spitzer/IRS. Therefore both the quantity and temperature of the dust particles are highly uncertain. Scientific motivation for the proposed observations include (1) improvement of our understanding of properties of debris disks at young main sequence stars, (2) provision of a set of relatively bright debris disks for study with ALMA, (3) provision of knowledge of the dust properties for stars with companions, regardless of whether the companion is stellar or planetary; in the case of planetary companions, many of our proposed Herschel target stars will be observed with the extreme adaptive optics systems SPHERE and/or GPI.

Lead Scientist: Ben Zuckerman

Allocated time: 10.7 hours

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A deep Herschel PACS imaging survey of transitional disks

We propose to observe with Herschel PACS a sample of 64 candidate transitional disks around young stars with the goal of characterising their disk geometry and relate it to the physical processes ruling disk evolution. The defining characteristic of transitional disks is a reduced opacity in the inner disk, indicating the onset of the disk dissipation phase and thought to represent an intermediate evolutionary state between primordial and debris disks. They constitute the last stage where gas and dust are available to form planets, and therefore their study is of extreme value in understanding planet formation including the formation of our own Solar System.

The sample of candidate transitional disks we propose to observe has been selected from a compilation of all the Class II young stellar objects members of nearby young clusters and associations, with known spectral types and spectral energy distributions complete up to the mid-IR. Our survey will greatly enrich the Herschel archive by extending current observations of transitional disks to a larger range of stellar masses, ages, and environments, as well as in sensitivity.

Using PACS photometry we aim at characterising the disk structure and geometry for this large sample of transitional disks, to study possible correlations of the disk parameters with their host star and environment. By combining Herschel data with complementary diagnostics (accretion rates, dust masses, multiplicity) we will determine the likely causes for disk clearing, to ultimately learn about the processes of disk evolution leading to planet formation.

This proposal is the last chance to acquire the far-IR information needed to fully exploit the scientific potential of our sample of candidate transitional disks in the coming decades. These objects are central to the understanding of disk evolution and the earliest stages of planet formation, and therefore the observations we propose have a high legacy value.

Lead Scientist: Catarina Alves de Oliveira

Allocated time: 22.2 hours

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A Search for C II Around Dusty A-Type Stars

We propose to obtain PACS C II 157.7 micon line spectra of 10 bright debris disks around dusty, A-type stars (with 70 micron fluxes >0.4 Jy) that are expected to be gas-rich if circumstellar gas in debris disks is generated via collisinal vaporization and/or photo desorption. C II is expected to be the dominant cooling line in debris disks. The high luminosity and UV flux of A-type stars is expected to efficiently produce second-generation gas. We plan to (1) constrain directly the gas:dust ratio in debris disks, (2) test models for the production of second-generation gas from circumstellar dust, and (3) extrapolate the composition of undetected parent bodies. Since the C II line emission from debris disks is relatively faint, PACS is required to conduct these observations

Lead Scientist: Christine Chen

Allocated time: 7.3 hours

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Environmental impact on planetary systems in the rich alpha Per cluster

The environment in which a star forms can potentially have a significant effect on the final planetary system that forms around it. We have recently carried out a WISE survey of the nearby, rich, young alpha Per cluster, a cluster essentially not observed with the Spitzer Space Telescope. Our findings suggest that this cluster is deficient in debris disks relative to other clusters in the same age range. We propose to use Herschel/PACS observations of WISE-detected alpha Per debris disks to determine if their distribution in semimajor axes is consistent with dynamical interactions as a principal cause of the low alpha Per debris disk fraction.

Lead Scientist: Carl Melis

Allocated time: 2 hours

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PACS photometry of water-rich protoplanetary disks

A major breakthrough in addressing the connection between disks and planets occurred in 2008 with the Spitzer Space Telescope discovery of a forest of mid-infrared emission lines of water and other molecules emitted by a high percentage of protolanetary disks around young, low-mass stars. These molecular lines reflect the physical and chemical state of the disk, and can be used in concert with disk models to study disk physical and chemical diversity in greater detail than ever before. In particular, our team is mapping the distribution of water vapor, to determine where and when planetary cores condense, and searching for the reason behind observed chemical variations between disks. A major, but not insurmountable, difficulty in the interpretation of the molecular emission from disks is the significant degree of degeneracy in disk models. The way around this difficulty is to obtain detailed multi-wavelength datasets. The far-IR region is especially crucial, as the dust here transitions from optically thick to thin, and emission depends sensitively on the temperature and density structure of the dust. We therefore propose here to complete the census of PACS photometry for emission-rich disks.

Lead Scientist: Colette Salyk

Allocated time: 2.9 hours

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HIFI CO observations of protoplanetary disks with molecular winds

We propose to use HIFI to observe resolved CO rotational line emission from a newly-identified class of disks --- the ``disk wind'' sources. These disks have emerged as a possible link between disks with envelopes and large outflows, and older, exposed and quiescent disks, and as such offer exciting potential for new discoveries. Multiple lines of evidence suggest that these disks produce significant wide-angle molecular winds, distinct from the jet-driven outflows observed in younger sources, but the detailed structure of this wind, and its launching mechanism, remain unknown. We propose here to observe resolved CO 14-13 line profiles with HIFI from 2 disk wind sources and a reference classical disk, to provide information complementary to that provided by an extensive existing multi-wavelength dataset. In particular, high-excitation CO rotational lines, like CO 14-13, probe a distinct temperature and density regime in the disk and wind, sensitive to the few-10 AU region, which cannot be otherwise probed from ground-based observatories.

Lead Scientist: Colette Salyk

Allocated time: 38.1 hours

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PACS Photometry of Transiting-Planet Systems with Warm Debris Disks

Dust in debris disks is produced by colliding or evaporating planetesimals, the remnant of the planet formation process. Warm dust disks, known by their emission at =<24 mic, are rare (4% of FGK main-sequence stars), and specially interesting because they trace material in the region likely to host terrestrial planets, where the dust has very short dynamical lifetimes. Dust in this region comes from very recent asteroidal collisions, migrating Kuiper Belt planetesimals, or migrating dust.

NASA's Kepler mission has just released a list of 1235 candidate transiting planets, and in parallel, the Wide-Field Infrared Survey Explorer (WISE) has just completed a sensitive all-sky mapping in the 3.4, 4.6, 12, and 22 micron bands. By cross-identifying the WISE sources with Kepler candidates as well as with other transiting planetary systems we have identified 21 transiting planet hosts with previously unknown warm debris disks.

We propose Herschel/PACS 100 and 160 micron photometry of this sample, to determine whether the warm dust in these systems represents stochastic outbursts of local dust production, or simply the Wien side of emission from a cold outer dust belt. These data will allow us to put constraints in the dust temperature and infrared luminosity of these systems, allowing them to be understood in the context of other debris disks and disk evolution theory.

This program represents a unique opportunity to exploit the synergy between three great space facilities: Herschel, Kepler, and WISE. The transiting planet sample hosts will remain among the most studied group of stars for the years to come, and our knowledge of their planetary architecture will remain incomplete if we do not understand the characteristics of their debris disks.

Lead Scientist: David Ardila

Allocated time: 21.1 hours

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Direct measurements of the warm gas distribution and vertical temperature gradient in protoplanetary disks.

Recent observations of protoplanetary disks with Herschel have revealed the presence of high-J CO lines. State-of-the-art disk models predicts that this emission arises from intermediate layers below the disk surface and above the mid-plane. These layers are shielded from the photodissociative (UV) radiation emitted by the pre-main-sequence star and are thus very important for the chemical evolution of the disk. Previous observations with PACS allows us to determine the temperature and density of the gas in these layers. The low-resolution spectra of PACS, however, does not provide direct information on the distribution of the gas. We propose follow-up observations with HIFI of the J=16-15 CO line previously detected with PACS in 8 disks. The high-spectral resolution of HIFI will allow us to directly measure the radial distribution of the emitting gas. This modest (14 hours) HIFI proposal will complement the previous PACS observations allowing to fully characterize the properties of the warm gas (temperature, density and radial distribution). The second goal of this project is to address the vertical temperature gradient inside the disk. This will be achieved by comparing the HIFI observation of CO J=16-15 line to spectrally-resolved ro-vibrational and low-J CO emission lines observed from the ground. For this we will implement thermo-chemical disk models developed in our group. We also propose follow-up HIFI observations of the strong [CII] emission detected with PACS in three protoplanetary disks. According to disk models this line is expected to emerge from the ionised disk surface of the disk and is linked to the CO chemistry (photodissociation). However, the measured line flux in HD 100546, HD 97048 and IRS 48 is high and might not all come from the disk but rather from an outflow or a remnant envelope. HIFI will allow to resolve to resolve the velocity profile of the line and in turn to disentangle its origin.

Lead Scientist: Davide Fedele

Allocated time: 14.4 hours

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Warm A Star Debris Disks from WISE

Debris disks trace the collisional breakdown of asteroid and comet parent bodies orbiting nearby main sequence stars. Debris disks are typically cold analogs of our Kuiper belt with emission peaking near 70 microns wavelength. However, a relatively small number of warm disks are known with emission at 22 - 24 microns. These systems are especially interesting because they trace dust in the region likely to host terrestrial planets, where the dust has a short dynamical lifetimes. They also tend to be young systems aged < 1 Gyr. This knowledge of warm debris disks - extrasolar analogs to our solar system's Zodiacal cloud - is based on the 25 year old IRAS survey and observations of selected targets with ISO and Spitzer.

The Wide-Field Infrared Survey Explorer (WISE) has recently completed new, sensitive all-sky mapping in the 3.3, 4.6, 12, and 22 micron bands. Association of the WISE sources to Hipparcos and Tycho stars has led to the identification of 61 nearby main sequence A stars with robustly detected warm 22 micron excesses not previously known. To determine whether these systems represent outbursts of asteroidal dust production (such as in the HD 69830 system), or simply the Wien side of emission from a cold outer dust belt, photometry at longer wavelengths is needed. We propose Herschel/PACS 70 and 160 micron photometry of this unbiased sample of new A star debris disks. These data will allow us to fully characterize the dust temperature and infrared luminosity of these systems, allowing them to be understood in the context of other debris disks and disk evolution theory. Herschel OT1 observations of FGKM stars from this survey show a 90% detection rate for 70 micron excess emission. The results from these combined samples will strongly constrain our picture of the collisional history of inner planetary systems.

Lead Scientist: Deborah Padgett

Allocated time: 32.5 hours

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Low gas to dust ratio in protoplanetary 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.

This proposal was ranked B for the OT1 period. We resubmit an updated version.

Lead Scientist: Edwige chapillon

Allocated time: 5.3 hours

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Do Debris Disks With Warm Dust Have A Cold Origin?--Searching For The Outer Planetesimal Belts

We propose Herschel dual-band PACS photometry for a unique set of 31 (B8—K0) stars that host on-going activity in the terrestrial planet zones, to probe for signatures of cold/outer planetesimal belts. We are interested in probing a fundamental question about planetary systems–is a two-belt structure like that of the solar system the most common outcome of planet formation? These young solar- and A-type have dust emission well characterized with Spitzer/IRS 5-35 micron spectroscopy, revealing dust regions similar in temperature to our asteroid belt and the interior zodiacal cloud (T∼150–200 K). Because the warm belts have a median temperature of ∼190K, slightly warmer than that expected at the snow line, we have reason to believe that there is a common grain creation mechanism operating in the inner regions of the star-disk systems. Herschel provides the observational sensitivity at PACS 70 (or 100) micron required to successfully constrain the extent of the inner/warm dust emission, or reveal the presence of an outer/colder belt of planetesimals. In summary, the PACS observations will: 1) detect the long wavelength emission of the warm/inner dust and/or establish the existence of an outer/colder planetesimal belt; 2) constrain via modeling properties of the emitting dust; e.g. charateristic temperature, minimum mass and position; 3) facilitate comparison of dust distributions across stellar spectral range; and 4) establish the overall architecture of the circumstellar dust, perhaps pointing to favorable regions where exoplanets may reside. We request 35.2 hours in PACS AORs using the mini-scan map mode for point-sources, selecting the blue (60–85 micron) filter for most (26 of 31) targets, and the green (85–125 micron) filter for 5 targets with Spitzer 70 micron detections in agreement with the short-wavelength warm-fit extrapolations.

Lead Scientist: Farisa Morales

Allocated time: 34.5 hours

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Constraining the Long Wavelength Emission of Two-Belt Debris Disks

We propose Herschel dual-band PACS photometry for a unique set of 20 stars that host on-going activity in the terrestrial planet zones and evidence of an outer/colder dust component, to continue the exploration, begun with Spitzer, of their disk structure and composition. The 20 solar- and A-type stars in this sample have combined Spitzer IRS+MIPS (5 to 70 µm) SEDs suggesting a two-ring disk architectures that mirror that of the asteroidal-Kuiper belt geometry of our own solar system. However, the extents of the outer zones are unconstrained due to the lack of data beyond 70 µm. Also, because the warm belts in our sample—across the B8 thru K0 stellar spectral range—have a median dust temperature of ∼190 K, slightly warmer than that expected at the snow line, we have reason to believe that there is a common grain creation mechanism operating in the inner regions of the star-disk systems, perhaps related to icy planetesimals in a cold outer regions. Herschel provides the observational sensitivity at PACS 100 and 160 µm required to successfully constrain the long wavelength emission of the outer/cold disks, and possibly resolve a subset of them. In summary, the PACS observations will: 1) establish the characteristic dust temperature of the outer/cold belts and constrain the minimum mass and position of the debris rings; 2) possibly resolve the spatial extend of a subset of systems; 3) advance our understanding of dust particle composition by constraining the long wavelength emission; 4) facilitate comparison of dust distributions across stellar spectral range; and 5) establish the overall architecture of the circumstellar dust, perhaps pointing to favorable regions where exoplanets may reside. We request 8.0 hours total in PACS AORs using the mini-scan map mode for point-sources, selecting the green (85–125 µm) and red (125-210 µm) filters to constrain the long wavelength emission for all targets.

Lead Scientist: Farisa Morales

Allocated time: 8 hours

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Debris Disks around Low-Mass Planet-Bearing Stars

Follow-up Herschel observations have recently confirmed the presence of a resolved debris disk around GJ 581, a nearby M star with 4 low-mass (super-Earth) planets. Debris disks around M stars are exceedingly rare (~1% detection rate in the DEBRIS survey), raising the question of whether the debris might somehow be directly related to the neighboring planets. In order to assess whether low-mass planets are strongly correlated with dusty debris or whether this is just a chance coincidence, we propose to dramatically increase the number of planet-bearing M stars observed by Herschel, from the current 3 up to a total of 20 stars. The proposed PACS 100/160 um images of 17 planet-bearing M stars will clarify whether this class of system preferentially has orbiting debris. Should any new disks be detected, the close proximity of the target M stars (~10 pc) makes them favorable candidates for resolved imaging, which may help to explain the unusual asymmetry in GJ 581's similarly resolved disk.

Lead Scientist: Geoffrey Bryden

Allocated time: 17.1 hours

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A PACS Spectroscopic Survey of the Chemistry of Transition Disks

In the past decade, transition disks have emerged as the first possible, measurable signposts of planets that have already or are in the process of forming. Recent detections of planetary mass objects within the inner holes of two transition disks definitively link the presence of disk holes with planet formation. However, these transitional disks have so far not yet been studied much in the warm molecular gas of a few 100 K, which connects the cold bulk mass of the outer disk (probed in the sub-mm) with warm inner regions (probed in the near-IR). The structure of transition disks is typically measured from the shape of the spectral energy distribution or the spatially imaged dust. Although the gaseous disk can be more difficult to study, the structure and chemistry of gas will provide significant constraints on the prospects for the final abundances and continued growth of gas giant planets. Herschel PACS offers a unique possibility to study the mid-J to high-J lines of CO together with lines of OH and water. These lines are predicted to emerge from the inner few tens of AU. Here we propose a deep search for molecular emission in PACS spectra of 12 of the most exciting transitional disks, two of which are already approved for ALMA observations. These PACS observations provide diagnostic information on the structure and chemistry of the warm gas that is needed to constrain models of gas in transition disks and to understand the connections, if any, between the gas in the inner and outer disk.

Lead Scientist: Greg Herczeg

Allocated time: 26.4 hours

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Debris Disks as a Tracer of Star and Planet Formation in Binaries

We propose to observe nearby binary star systems to discover and characterise circumbinary debris disks. With these data we will study the effects of cluster evolution and long term stability on planet formation. The primary goal is to resolve disks, which allows an analysis of the binary and disk orbital planes and leads to conclusions about the formation and stability of the system. The secondary goal is to test whether dust resides in unstable regions, which could be the result of a dynamical instability induced by perturbations from the binary. Both goals focus on the dynamics of circumbinary debris, and provide information on planet formation and survival in binary systems.

Lead Scientist: Grant Kennedy

Allocated time: 11.4 hours

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Disk evolution in a cluster environment - PACS and SPIRE imaging of the LkHa198/V367 Cas region

We will do sensitive PACS and SPIRE observations of the LkHa198/V376 cluster to find all young stars, determine their disk/envelope masses and the star formation rate in the cloud.

Lead Scientist: Goeran Sandell

Allocated time: 1.5 hours

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The Masses of Brown Dwarf Disks and the Disk-Stellar Mass Scaling Relation

Theoretical models of planet formation have shown that the masses of protoplanetary disks, which are dominated by gas, strongly affect the resulting planetary architectures. Expanding upon the Herschel KP "Gas in Protoplanetary Systems" (GASPS), we propose here a sensitive Herschel/PACS survey to measure the gas disk masses of a well-characterized sample of very low-mass stars/brown dwarfs (BDs). Our survey has two main goals. First, we will empirically set a limit for the largest planets that can form around BDs and thus elucidate the nature of the few planet candidates discovered around them. Second, we will combine our mass estimates with those acquired within GASPS for intermediate- and solar-masss stars to constrain how the disk mass scales with the mass of the central star. To reach these goals we will use deep PACS exposures to detect the [OI] 63 micron emission line which traces the bulk of the disk mass residing beyond tens of AU from young stars. We will use similar models to those developed within GASPS to convert [OI] line fluxes into gas masses. The sensitivity of Herschel/PACS gives us a unique opportunity to measure disk masses down to the BD regime and to provide the critical observational constraints to planet formation theories.

Lead Scientist: Ilaria Pascucci

Allocated time: 46.1 hours

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Characterizing nearby WISE warm debris disks with Herschel

Until recently, debris disk identification and study has been accomplished mostly with the 30 year old IRAS all-sky survey (and small number of pointed observations by Spitzer) and it has been limited to larger cold disks. Study of warm debris disks can provide important information concerning terrestrial planet formation and evolution, however, their identification and characterization has been restriected to a very small number of discovered warm debris disks (N<10). The Wide-Field Infrared Explorer (WISE) has surveyed the entire sky at mid-IR wavelenghts, and the WISE survey provides almost 100 times better photometric sensitivity than IRAS and approximately 10 times betterpositional accuracy. Using this improved information and sophisticated target selection criteria, we have identified a complete, well-defined group of 30 nearby (d < 100 pc) Hipparcos main-sequence stars showing the indication of warm debris disks. With nine of these stars being observed as part of an existing Herschel program, we propose to observe the remaining 21 stars to complete a census of warm debris disks in the solar neighborhood. With Herschel PACS measurements at 70 and 160 micron, we can fully constrain dust temperature and dust quantity around this rare group of stars.

Lead Scientist: Inseok Song

Allocated time: 8.5 hours

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Cataloging Debris Disks within 100pc

Although many hundreds of debris disks have been discovered over the past three decades, these stars are widely diversed in terms of ages, distances, reliabilities, levels of dust characterization, etc. Nearest debris disks are most interesting because they are brighter and larger than more distant similar debris disks. By collecting all known debris disks in the literature, we re-analyzed all debris disks (about 1800) in a homogeneous way using the state-of-the-art photosphere fitting method and including the newest available data including WISE. Out of this reanalysis, we selected 123 nearby (d<100[c) bona-fide debris disks where almost a half of them have a dust excess measurement at only one passband. To constrain dust properties for these nearby debris disks, we request to obtain 100 and 160 micron measurements with Herschel/PACS. The result of this proposed study will be a complete inventory of known debris disks within 100pc with fully constrained dust properties. Such an inventory will be an indispensable asset for any future debris disk studies with ALMA, SOFIA, SPICA, etc.

Lead Scientist: Inseok Song

Allocated time: 10 hours

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Beyond the Snow Line: the Oxidation State of Disks and Connections to the Transport and Growth of Icy Bodies

Herschel offers an unique opportunity to probe the conditions and chemical evolution in the planet formation region of disks, particularly at radii immediately beyond the snow line (~ 1 to 20 AU), the formation zone for asteroids and gas giants in the Solar system. We propose PACS spectroscopy of a small sample of T Tauri star disks in order to investigate the oxidation state of the gas at these radii, a key parameter in gas-phase chemistry and solid-state mineralogy. The proposed data will provide an important observational link between the oxidation conditions implied by known meteoritic properties and T Tauri disks as proxies for the conditions in the early solar nebula. Results from Spitzer already suggest variations in the oxidation state of the warm gas interior to the snow line, based on the observed range in the content of simple organic molecules relative to water. This could result from different efficiencies in planetesimal growth and sequestration of water ice beyond the snow line, differences potentially related to the mass of the disk. The oxidation state outside the snow line is influenced by the radial transport of water vapor and ice, settling and turbulence, and the growth of large icy bodies. The action and efficiency of these processes can leave their imprint on the C/O ratio of gas in the disk atmosphere, with predicted changes in the chemistry. We propose to carry out sensitive PACS spectroscopy of chemical signatures (CO, NH3, HCN and H2O) that can probe the oxidation state at 1-20 AU. The targets are carefully picked to sample a range in disk mass and organic disk signatures inside of the snow line. The combination of Herschel and Spitzer data will allow us to compare the chemistry interior and exterior to the snow line and to better understand the role of physical processes such as the radial migration and growth of icy bodies that affect disk chemical evolution and planet formation.

Lead Scientist: John Carr

Allocated time: 43.1 hours

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The Origin of the Destroyed Planetary Body at G29-38: One of Many Asteroids or a Major Rocky Planet?

G29-38 is the prototype and brightest example of a white dwarf orbited by rocky debris from a tidally-destroyed planetary body. Because this warm debris orbits within 1 solar radius, the parent body must have originated in a more distant region. Thus, we suspect a persistent planetesimal belt at G29-38, that contains a substantial number and mass of remnant planetary bodies, as this best accounts for the larger family of disk- and metal -polluted white dwarfs. We propose Herschel PACS observations to detect cold dust from within this remnant population of minor planets. A lack of cool dust favors a scenario in which the observed warm dust resulted from the tidal destruction of a major rocky planet. The proposed observations are the best chance to detect such a cold disk around any metal-enriched white dwarf, and will provide insight into the fate of planetary systems at A- and F-type stars.

Lead Scientist: Jay Farihi

Allocated time: 9.4 hours

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Confirmation and characterisation of two debris disks around low-mass stars.

Debris disks surrounding main sequence stars are analoguous to the Kuiper Belt around the Sun and are signposts for exoplanetary systems according to planet formation theory. Low-mass stars (M-stars) are challenging targets for both exoplanet searches and debris disk searches. However, they are vital for understanding planet formation in complement of higher mass stars. With Herschel, we propose to confirm and characterise two M-star candidate disks while only two others are presently known among low-mass stars.

The two M-stars, GJ842.2 and HD95650, have candidate disks from SCUBA and Spitzer observations. We propose to make PACS images that are deep enough to detect their photospheres in order to verify unambiguously position coincidence between stars and disks. This approach could not be accomplished by neither SCUBA nor Spitzer. Additionally, it is reasonable to speculate that these disks will be large enough to be resolved by PACS providing definite proof of their nature. Finally, we request SPIRE in complement to PACS to fully sample the SED of the dust emission in order to determine their fractional dust lumninosities and dust properties.

One of the key question in debris disk studies today is to understand the physics responsible for the trend apparent in their detection fractions indicating fewer debris disks around lower-mass stars. Several physical clues have been suggested; for instance, observed and theorised lack of massive gaseous planets around M-stars could reduce disk stirring and so dust production. It is vital to expand the number of known disks around M-stars to tackle this key question. By resolving two new disks and modelling their images, we shall infer the scale of the planetary systems around M-stars and be able to measure the size of the inner hole hosting planets. Asymmetries in their images would be indicative of resonances with planets. The scarcity of known disks around M-stars makes these observations crucial.

Lead Scientist: Jean-Francois Lestrade

Allocated time: 6.5 hours

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Search for Edgeworth-Kuiper Belt Analogs in the Alpha Perseus Cluster

Advances in understanding planet formation and evolution can be gained from studying how frequently debris disks form and how they interact in different environments over time. While field stars near Earth enable small quantities of dust to be detected, the nearest rich open clusters -- with their well constrained ages -- enable one to infer how debris disk characteristics evolve with time as a function of spectral type and birth environment. Located ~172 pc from Earth, the ~60 Myr old Alpha Perseus cluster is the only substantial and nearby young open cluster or moving group that was not targeted by the Spitzer Space Telescope, yet its richness provides an excellent laboratory to address fundamental, debris disk-related, questions. Recently we identified a dozen or so Alpha Per members to have mid-IR excess based on the published WISE catalog. Previous studies of debris disks have demonstrated that significantly more stars have dominant excess emission at 60 micron than at mid-IR wavelengths, implying the potential presence of a large population of stars with cold debris disks -- analogous to the Sun's Edgeworth-Kuiper Belt -- in Alpha Per. We propose to observe 97 early-type members of Alpha Per with PACS at 70 and 160 microns; these will provide far-IR photometry for a complete sample of known Alpha Per A- and F-type stars.

Lead Scientist: Joseph Rhee

Allocated time: 17.7 hours

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The distribution of water vapor in protoplanetary disks and their winds

One of the key mission objectives of Herschel is to understand the role of water vapor in various environments, including in protoplanetary disks. Water has an immediate relevance to the formation of planets and to our own origin. We propose to obtain deep PACS/SPIRE line spectra of water, OH and CO in protoplanetary disks selected to have strong rotational water vapor emission at mid-infrared (10-36 micron) wavelengths (the newly discovered mid-infrared molecular forest). The mid-infrared lines trace warm to hot gas formed within a few AU from the central star. The proposed observations will relate the oxygen chemistry and transport of water in the inner few AU with that of the cooler outer disk - 1-100 AU - as traced by the PACS water lines. The Spitzer observations suggest that water vapor may be strongly depleted in the disk surface beyond 1 AU although gas and dust temperatures are high enough to maintain abundant water in the surface out to at least 10 AU. It is not understood whether this is due to chemical effects, radiative transfer effects or whether the water vapor can diffuse downwards to colder layers where is can freeze out and settle to the midplane. Measuring the radial abundance structure of the water emission by combining Herschel and Spitzer spectroscopy of water vapor is a critical step to distinguish between these scenarios and to constrain detailed disk models. Based on model fits to the mid-infrared lines, we predict very strong differences in the 50-200 micron water lines, depending on the distribution of water in the outer disk surface. We requested time to observe 8 disks in OT-1, but were awarded time for 4. This is a proposal for time to observe the remaining 4 in order to gain statistical confidence across a range of disk accretion rates and to probe the influence of disk winds on the properties of the distribution of water vapor.

Lead Scientist: Klaus Pontoppidan

Allocated time: 42 hours

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The Final Four: Completing Herschel's Imaging Legacy for Key Debris Disk Systems

Debris disks are the signposts of planetary systems: collisions among asteroidal and cometary parent bodies maintain the observed dust population against losses to radiation pressure and P-R drag. While hundreds of debris disks are known from far-IR excecss emission around main sequence stars, the best- understood systems are the ~20 that are spatially resolved. Disk images establish the size scale of an exoplanetary system. They can reveal central holes, rings, gaps, warps, and asymmetries in the dust distribution which indicate the presence of planetary perturbers. Disk images at different wavelengths are sensitive to dust grains of different sizes, and thus provide a way to trace dust transport and segregation processes.

In spring 2011 we discovered large new debris disk in HST coronagraphic images. The new system is an eccentric ring with a sharp inner edge and cleared central zone, and thus is remarkably similar to the classic Fomalhaut debris ring. Spitzer only detected the system at a single wavelength. We propose PACS and SPIRE imaging photometry to fully establish the spatial and spectral properties of this new debris system, and of three other HST-detected debris disks that lack Herschel measurements. Simultaneous modeling of the far-IR images, SEDs, and HST images of these disk will provide important constraints on the physical properties and dynamical state of their constituent dust. Our small program will complete Herschel's legacy dataset for the key subsample of bright disks that are detected in scacttered light,

Lead Scientist: Karl Stapelfeldt

Allocated time: 3.7 hours

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Characterization of Outer Exoplanetary Systems With Herschel Imaging

Our knowledge of planetary systems outside of ours is confined almost entirely to cases where the planets are close to the star. A critical stage in the development of the Solar System was the stabilization of the orbits of Jupiter and Saturn far from the Sun. What are the characteristics of other planetary systems at large radii? Planetary debris disks provide our best tool to answer this question. However, our interpretation of these systems is currently crippled by the lack, in most cases, of more information beyond a few photometric points on a spectral energy distribution. Such data can be fitted by a broad variety of quite different disk models. Resolved Herschel images of disks can provide much better constraints on models and can lead to sufficient understanding of the general behavior to help interpret even those systems where resolved images are not possible.

We have identified 17 bright disks that show marginally resolved structures in Spitzer data, suggesting a radial size of cold planetesimal belt 3 to 10 times larger than our own Kuiper Belt. Since the disk mass is proportional to the disk diameter and covering factor of the dust, these systems are likely to be associated with the most massive planetary systems, making them the possible sites where the richest, most massive and extended families of planets will form. We propose to image these disks that can be resolved well at PACS 70 micron but not in any existing Herschel programs. We will use the resolved images as well as the photometric data obtained with SPIRE to probe: (1) the properties of cold planetesimal belts as signposts of ice giants at large orbits, and (2) the diversity of outermost planetesimal zones around other stars and the underlying causes.

Lead Scientist: Kate Su

Allocated time: 13.7 hours

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A Sensitive Search for OH and H2O in the Cold Outer Layers of Planet-forming Disk

One of the biggest results that have come from Herschel HIFI is the detection of cold water vapor where it would otherwise be frozen onto grains (Hogerheijde et al. 2011, Bergin et al. 2010). Surprisingly, one unexpected inference of these observations is the requirement that the photo-desorption of water be reduced by nearly an order of magnitude to reproduce the emission line observations. The interpretation of these results was the existence of a population of `dry' (reduced water-ice-coated) grains on the surface of the disk. Emission line data, however, is intrinsically model dependent with many uncertainties, even in the collisional rates. We propose here a test of the models used to reproduce the Herschel observed water emission using an absorption line study of the main photo-desorption products of water, namely gas-phase H2O and OH. This type of study is intrinsically more sensitive as it is a direct measure of the column, without the need to assume anything about the excitation conditions. Both H2O and OH are expected to be predominantly in the ground state, and therefore such a study is the only direct test of the bulk-water-vapor reservoir. This program is designed to optimize the opportunity to find water and OH in a T Tauri disk both with the ideal inclination and continuum. These results will robustly test theories of water formation in disk systems, namely the presence of a cold, UV-photodesorbed layer of water vapor sitting on the disk surface as inferred by Herschel emission measurements of T Tauris.

Lead Scientist: L. Ilsedore Cleeves

Allocated time: 11.8 hours

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Probing the Dominant Ion on the Surface of Planet-Forming Disks with Herschel/HIFI

C+ is expected to be the dominant ion tracing the ultraviolet (UV) radiation exposed layers of young T Tauri disks. However, observational evidence of its existence has thus far eluded us. Current Herschel Key Programs using PACS include the detection of C+ as a key program facet; however, these studies have faced substantial difficulties (galactic background, strong continuum/narrow line width) in their ability to detect this intrinsically weak line. We have designed an optimized Herschel HIFI program to finally detect this line in a sample of disk systems which span a range of dust settling, and thus a range of gas mass exposed to UV radiation. This will provide a Herschel legacy product to test models of UV radiation transport and the resulting chemistry. This lies at the heart of the detailed models of disk chemistry. Therefore, this information will be crucial as we enter the era of ALMA, where resolved observations will require sophisticated modeling to interpret.

Lead Scientist: L. Ilsedore Cleeves

Allocated time: 14.4 hours

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Tracing protostellar disk ionisation with far-infrared lines

Protoplanetary gas and dust disks around T Tauri stars are the most important elements in the process of planet formation. In particular, the dissipation time scale of disks sets a critical time limit for planet formation. The mechanisms of disk dissipation are poorly understood, however. Apart from the planet formation process itself, photoevaporation and disk instabilities induced by the magneto- rotational instability are key candidates. In both cases, heating and ionisation by stellar short-wavelength radiation plays a crucial role. High-energy stellar radiation (X-rays, extreme ultraviolet) also drives chemical networks in circumstellar disks, forming key molecules that eventually become important for the formation of life in habitable zones. However, there is little information on the X-ray radiation spectrum impinging on the disk, given various sources of photoelectric absorption. We will study disk ionisation and X-ray driven chemistry by observing X-ray sensitive lines in an outstanding and unique sample of three classical T Tauri stars in which X-rays appear to be blocked before reaching the disk. We will compare the results with a control sample of disks that appear to be irradiated by high levels of stellar X-ray radiation. Our X-ray sensitive lines include transitions from HCN, HCO+, and ortho-NH3. The interpretation of our results will be based on thermo-chemical codes developed in the proposing team.

Lead Scientist: Manuel Guedel

Allocated time: 2.2 hours

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A deep HIFI search for cold para-water vapor in three protoplanetary disks

Using the HIFI spectrometer on the Herschel Space Observatory we have detected the ground state lines of cold water vapor in the outer reaches of the disk around the nearby young star TW Hya. Only UV-induced photodesorption of water molecules off icy grains can explain the presence of water vapor in these cold regions. The lines of ortho-H2O 110-101 and para-H2O 111-000 are weaker than expected, suggesting that up to 80% of the larger, icy grains have settled out of the ultraviolet's reach toward the midplane, representing a 'hidden' reservoir of thousands of Earth Oceans. Analysis of the line strengths revealed a water ortho-to-para ratio of 0.77, much lower than found in Solar System comets (1.5-3), leading us to suggest that comets consist of ice mixtures from across the full extent of the Solar Nebula and implying long-range mixing of icy material in disks.

We have been awarded 47 hrs in Herschel OT1 to search three more gas-rich protoplanetary disks for the presence of ortho-H2O 110-101 at 557 GHz with HIFI (DM Tau, HD100546, and AA Tau). These targets represent, after TW Hya, the closest, mostly likely candidates to detect these weak lines.

For OT2 we propose an equally deep search for the para-H2O 111-000 line at 1113 GHz to these same three targets. These proposed observations form a unique legacy of Herschel and HIFI: together with our OT1 data, they will provide a complete inventory of cold water in these disks; they will allow us to investigate if low ortho-to-para ratios are common in protoplanetary disks or unique to TW Hya; and they will provide unparalleled insight into the origin of the Earth's oceans and the possibility of ocean-covered worlds elsewhere.

Lead Scientist: Michiel Hogerheijde

Allocated time: 87.6 hours

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Confirming a sample of massive and luminous debris disks identified in the Herschel-ATLAS

Debris disks are the remains of planetary system formation, tracing the existence of planetesimal-sized objects in orbit around main sequence stars. Current and planned surveys of debris disks (including the Herschel Key Projects DEBRIS and DUNES) are deep surveys aimed at characterising the typical population of disks and targeted at samples of a few hundred nearby objects. These deep narrow surveys are relatively insensitive to the rarities in the debris disk population, some of which may be luminous and/or massive disks that have undergone recent disruptive collisional events. We have recently shown that the primarily extragalactic Key Project, the Herschel-ATLAS, can be used as a wide and shallow survey of debris disks by combining its excellent optical coverage and statistical techniques more commonly employed to identify galaxies. The combination of Herschel-ATLAS, DEBRIS and DUNES thus forms a powerful nested tier of surveys that will be sensitive to disks across the spectrum from exosolar analogues to rare disks that cannot be inferred from local populations. In this proposal we seek time to image 23 candidate disks that we have discovered in the Herschel-ATLAS with PACS so that we may confirm them as true debris disks and model their SEDs to extract mass, temperature and fractional luminosity. We will confirm whether these disk candidates are in fact the most luminous disks yet detected.

Lead Scientist: Mark Thompson

Allocated time: 19.5 hours

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Gas chemistry in the inner holes of planet-hosting transitional disks

T Cha, SR21 and HD135344B are transitional disks known to host potentially planetary-mass companions within their inner holes: NACO/SAM high angular resolution observations allowed us to detect and confirm an extremely red substellar companion located within the gap of the disc of T Cha. In the case of SR21 and HD135344B, detailed spectro-astrometric observations have revealed strongly in-homogenous warm CO-gas in the inner holes of the disks truncated close to the stars, which supports the presence of Jupiter-mass objects in the inner holes. This is supported by a tentative NACO/SAM detection of a companion candidate within the disk hole of SR 21. Therefore, we are witnessing in-situ formation of substellar objects within the disks of these three objects.

Since these disks lack of deep Herschel gas line observations, we propose to use the unique capabilities of Herschel to perform a detailed study of the gas content within the disks. This project will provide key constrains to understand the physics and chemistry that govern the early stages of planetary formation for years to come.

Lead Scientist: Nuria Huelamo Bautista

Allocated time: 22.8 hours

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HD 37594: An Exceptionally Massive Cold Debris Disc in the Solar Neighbourhood

HD 37594 is a seemingly ordinary A8 V spectral type star at a distance of 43pc from the Sun. Spitzer MIPS observations, performed as part of a volume-limited survey of A type stars at the end of the Spitzer cryogenic mission, have shown this star to harbour an exceptionally massive cold debris disc (dust mass and temperature approx. 0.04 Earth masses and 54K respectively). This is potentially the most massive debris disc around an A type star within 50pc of the Sun, a sample which includes well known systems such as Vega, Fomalhaut, beta Pictoris, beta Leo and beta UMa. HD 37594 exhibits no signs of youth, and its optical and near-IR emission suggests it to be a normal main-sequence star, with slightly below solar metallicity, and no warm excess emission. Currently the only observational data for this debris disc is MIPS photometry at 24 and 70 um; longer wavelength and higher spatial resolution observations are required to gain any insight into this system beyond ascribing a characteristic dust temperature and highly uncertain dust mass.

We propose to image this exceptionally massive debris disc with Herschel's PACS and SPIRE, to allow modelling by simultaneously fitting a well-sampled spectral energy distribution (SED) from 24 to 500um and the spatial flux distribution in high S/N 70-160um images.

Lead Scientist: Neil Phillips

Allocated time: 0.9 hours

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Dark shadows in T Tauri disks: accretion-related structural changes revealed by far-infrared variability

Some pre-main sequence stars exhibit peculiar wavelength-dependence of their mid-infrared spectral variability. This finding led to the proposal of a vertically extended obscuring structure in the inner part of the system that casts time-variable shadow on the outer disk. It is an extra component of T Tauri disks not considered in most disk models so far. In our previous optical-to-mid-infrared survey we could directly detect the thermal emission of this obscuring dust cloud. In order to initiate the physical characterization of the shadowing material, we propose a 70/160 um 4-epoch monitoring survey of eight young stars in the Chamaeleon I star forming region with Herschel. For half of this sample our earlier measurements already hint for the presence of a shadowing structure. Simultaneously with the Herschel observations we will also arrange optical-to-mid-infrared observations from the ground. We will perform a correlation analysis between the variability patterns observed at different wavelengths, in order to understand the origin of the obscuring structure. Correlation between optical and far-infrared light curves would favor an orbiting warp or long-lived dust cloud in the inner disk, while anticorrelation is interpreted as a signature of a temporary dust cloud lifted above the disk plane. In both scenarios the probable driving force behind the origin and the temporal rearrangement of this structure is time-variable accretion. Through detailed modeling of the spectral energy distributions and of the wavelength-dependence of the variability, basic physical parameters of the obscuring structure will be derived. Together with the timescale on which its structure can change, these are important entries to learn what kind of dynamical processes occur in the inner disks of low-mass pre-main sequence stars. For this project we request 7.8 h of Herschel observing time.

Lead Scientist: Peter Abraham

Allocated time: 7.8 hours

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Disk Structure and Evolution Around Very Low Mass Stars

We propose to observe the circumstellar disks around 28 very low mass stars that lie between the sub-stellar limit at 0.08 msun and 0.3-0.5 msun, the level where disks are bright enough to be readily detectable in the large, shallow Herschel surveys. The objects are located in 4 different star-forming regions that span a range of ages from roughly 1 - 3 Myr. This sample will provide the data necessary to link our understanding of disk evolution around solar-mass stars to those around sub-stellar objects, already well-represented by Herschel GT1 and OT1 programs. We will use proven disk modeling codes developed by team members and used extensively for modeling disks around stars and brown dwarfs. This approach has already worked well in our GT1 program on sub-stellar objects and in our first publication about its initial results.

Lead Scientist: Paul Harvey

Allocated time: 19.7 hours

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SPIRE Followup of Cold Disks Detected Around Brown Dwarfs at 160um

We propose SPIRE photometry of the brightest 8 brown dwarfs detected at both 70 and 160um in our GT1 program that has just completed observing 50 BD's. These 8 BD's are expected to be detected at 250-350um and half are also likely detectable at 500um. The addition of longer wavelength data for even this 20% of our sample will enable much stronger limits to be placed on the geometry of the outer disks, the grain size distribution, and the total disk masses. With the ultimate goal of adding ALMA photometry and imaging at longer wavelengths, we will be able to derive much more accurate physical parameters of the disks around these objects by using the entire SED from 1um to 1mm.

Lead Scientist: Paul Harvey

Allocated time: 2.6 hours

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Testing the Proposed Model: Detecting Disks around Nearby Carbon Dwarfs

With the discovery of G77-61 (Dahn et al. 1977) at a mere 58 pc and therefore relatively low luminosity, a category of dwarf carbon (dC) stars was finally recognized. This, however, presented a puzzle because a low mass star is incapable of the helium fusion needed to create the carbon seen in its atmosphere. A reolution was proposed and generally accepted a second member of a system could 'dump' carbon on it through an AGB stage into a circumstellar disk which would replenish the fully convective atmosphere in a reasonable period.

Current understanding of the formation and evolution of dC's is, however, limited by the small number of objects and observations. We propose observations of each carbon dwarf with Herschel PACS 100/160 um, to to detect the proposed redsidual circumstellar disk. The proposed model for creating carbon dwarfs is based on three objects and the mechanism for dumping material on these low-mass stars and building the debris systems are currently unexplored. Thus the opportunity afforded by thisr program to add observational proof is valuable, especially for the very ill-studied carbon dwarfs. Only Herscehl can provide the spectral range and sensitivity to gain the observations needed in understanding the cold circumstellar disk and dissipation timescales around evolved stars placing carbon in our ISM - a building block of life as we know it.

Lead Scientist: Patrick Lowrance

Allocated time: 14 hours

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Warm H2O in protoplanetary disks: a key study for telluric planet formation

One of the key questions dealing with the gas is how much water is present in disks and how widely is it distributed.

During the systematic data reduction of Herschel Space Observatory GASPS KP we have detected a water emission that was not expected. This line istracing warm, intermediate temperature (400 to 1000 K) water and could be the link between the Spitzer observations of hot water in disks in the mid-IR, from the inner most parts of the disk, and the observations of cold water with Herschel in the far -IR, tracing the outer regions of the disk. Our present sample of warm water detections have 10 targets with solid detections, i. e., 12% detection rate, and another 18 tentative detections, with signal-to-noise ratios between 2 and 3.

With the presental proposal we ask to spectroscopically observe the tentative detections in order to get the required sigma level for a solid detection. We ask for PACS line spectra for ten Taurus sources with tentative detections. If all the detections turn out ro be real, we will double the size of the sample and geta much larger detection rate of 28%.

Lead Scientist: Pablo Riviere

Allocated time: 28 hours

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Investigating the Architecture and Collisional State of Four Nearby Debris Disks with PACS/SPIRE Imaging

We propose sensitive PACS and SPIRE imaging photometry of four stars with important debris disks yet to be imaged with Herschel. Two of these stars (EF Cha and HD 165014) have warm debris disks *and* complex mid-IR spectral structures that provide evidence for critical terrestrial planet formation processes: the formation of large, differentiated bodies and terrestrial water delivery. Two (HD 15115 and HD 61005) have colder, extended Kuiper belt-like disks with newly discovered structures likely induced by massive jovian planets. Our PACS imaging of the first sample will help determine whether these terrestrial planet-forming systems also have Kuiper belts, features crucial to interpreting the planet-forming potential of these systems. Our PACS/SPIRE imaging of HD 15115 and HD 61005 will spatially resolve their disks to identify additional signatures of embedded planets and will constrain the disk far-IR slope and thus shed light on the collisional states of two debris disks perturbed by a planets.

Lead Scientist: Thayne Currie

Allocated time: 4.2 hours

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Remnant Gas Dispersal and Planet Formation: The Intriguing Case of the 10 Myr Old Transitional Disk of RX J1852.3-3700.

RX J1852.3-3700 is a nearby 10 Myr old 1.1 Msol T Tauri star, harbouring a well-characterized transitional disk with an inner hole in its dust disk corresponding to the Saturn/Uranus zone in our own solar system. Based on observational constraints on the CO and H2 gas mass, the disk is likely in the process of gas clearing. As part of our Herschel program to search for remnant gas in well-studied 10--150 Myr disk systems, we have recently detected [OI] 63 micron in this disk.

Based on the thermo-chemical disk models of Gorti & Hollenbach (2004), we have identified two possible disk configurations that could explain the observed [OI], are consistent with the non-detections of CO and H2, and that differ significantly in predicted radial extent, gas masses, inferred gas-to-dust ratios, which point at different scenarios for gas dispersal and prospects for planet formation.

We propose to obtain deep PACS spectroscopy of the [CII] 158 micron line, with the goal of constraining the spatial extent of the gas distribution, and thus discriminate between the two scenarios.

Lead Scientist: Vincent Geers

Allocated time: 1.6 hours

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