| Description |
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. |
