Herschel Space Observatory and the evolution of Gas in Disks

The Herschel Space Observatory is the European Space Agency's fourth "Cornerstone Mission" and deploys a passively cooled 3.5 meter telescope to observe the Far-infrared and Submillimeter Universe. Herschel is planned as a three year observatory mission, with a launch date planned for 2008. It will be launched on the same vehicle as the Planck mission, where both will orbit independently around the second Earth-Sun Lagrange point.

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We propose the first extensive, systematic survey of gas in circumstellar disks over the critical transition from gas-rich protoplanetary through to gas-poor debris. The brightest spectral lines from disks lie in the far-infrared and arise from radii 10-100 AU, 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.

We will carry out a 2-phase PACS study, surveying the fine structure lines of [CII]157um and [OI]63um in 274 objects, and following up the brightest sources with observations of [OI]145um and rotational lines of H2O. The gas mass sensitivity, a few 1e-5 Msun, will be more than an order of magnitude lower than achieved by ISO and Spitzer and expected for SOFIA. We will also measure the dust continuum to an equivalent mass sensitivity. Team members include experts in the modeling of disk structure, chemistry, and radiative transfer necessary to interpret these data.

We will observe nearby clusters in the age range 1-30Myr, encompassing disk masses 1e-2 - 1e-5 Msun, and stellar luminosity 1-100 Lsun. This covers the dominant epoch of planet formation and the mass from protoplanetary through to young debris disk. Furthermore our sample is chosen to include a wide range of X-ray & UV flux, and SED shape, from classical SED Class II, through "transition" disks with inner dust holes, to disks with small IR excesses. With this extensive dataset, our program will:

  • Trace gas and dust in the planet formation region across an extensive multivariate parameter space
  • Provide the first definitive measurement of the gas dissipation timescale in disks
  • Study the evolutionary link between protoplanetary and debris disks
  • Investigate the extent of warm H2O in the planet-forming regions of disks, with implications for the volatile content of developing planets
  • Provide an extensive database of disk observations and models with long-lasting legacy value for followup observations