| Description |
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. |
