Program: GS-2006A-Q-5

We propose to image with MICHELLE and T-ReCS at 10 and 18 microns a sample of 13 circumstellar debris disks, most of which have been observed by Rieke et al. using Spitzer. These observations will continue our exploration of the relationship between disk brightness, structure, and the occurrence of catastrophic planetesimal collisions and other types of major events and processes. Our previous Gemini imaging of Beta Pic, for example, showed that its debris disk has a strong wavelength-dependent brightness asymmetry, which we attribute to the release into the disk of a distinct population of dust particles by the recent catastrophic breakup of a planetesimal. The Rieke et al. Spitzer sample shows that the 24-micron emission attributable to a debris disk typically decreases with disk age, but within each age bin, they found a large range in the excess, which they propose is associated with stochastic processes, such as collisional planetesimal breakup, in the disks. Our Beta Pic study and that by Rieke et al. suggest that significant relationships may exist between disk mid-IR brightness (due, e.g., to the sudden creation of numerous small particles) and disk structure (e.g., asymmetries). One debris disk in our study, Zeta Lep, has now been clearly resolved at 18 microns with T-ReCS observations, and its extension implies a disk of a size comparable to our asteroid belt. The proposed observations in the continuation of this project will look at more young (<600 Myr) debris disks, mostly drawn from the Rieke et al. sample, to investigate the processes that are responsible for the observed structure in the disks.