Dr. Angela Cotera

December 20, 2006

"Solar Systems In Formation: A NICMOS Coronagraphic Survey of Protoplanetary and Debris Disks"


Current theories suggest that dust within the early protostellar envelope settles into the disk mid-plane resulting in a dusty circumstellar disk. The goal of HST GO 10177 is to identify and study stars surrounded by disks during what is presumably the planetary formation stage: the T-Tauri (ò1 Myr) to debris disks (ò10 Myr) phase. The observations are technically challenging at NIR and optical wavelength due to the high contrast between the bright central star and the faint disk, requiring observation with the NICMOS coronagraph. The observations are sensitive to the light scattered off the surrounding disk. In the mid-infrared (MIR, ò5-25 micron), recent advances in array technology combined with the availability of large ground-based telescopes (i.e. Keck and Gemini), have made possible subarcsecond resolution direct imaging of the cold dust disks around the types of stars included in the HST survey. The MIR radiation from disks is thermal radiation from dust heated by starlight and/or viscous accretion. Modeling of the MIR emission from previously detected disk (e.g. HR 4796A one of the first evolved disk to be observed by HST), provided compelling evidence that the dust encircles a solar-system-sized hole, within which a more tenuous concentration of hot dust remains close to the star, consistent with the results from HST/NICMOS coronagraphic images. Since different wavelength regions probe different properties of the evolving circumstellar environment, establishing a self-consistent understanding of the formation of these potential planetary systems requires that observations from one portion of the electromagnetic spectrum be reconciled with the results at other wavelengths.