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“The Evolution of Protoplanetary Disks, and the Formation of Giant Planets” Professor Dan Watson University of Rochester |
| With the Spitzer Space Telescope's Infrared Spectrograph, we have acquired mid-infrared (5-40 micron) spectra of large, complete samples of protoplanetary disks around stars of Solar type and smaller, in several nearby young clusters. These observations probe the structure and composition of solid matter in the planet-forming regions of the disks (r = 0.1-100 AU) and permit detailed characterization of the evolution of protoplanetary disks through the first few million years of system life: We find trends in vertical and radial structure, dust-grain growth, and dust-grain crystallization with cluster age, and strong correlation among these properties within given clusters. We also, surprisingly, find unexpected large variations in these properties within given clusters, and find that they are strongly un-correlated with other system properties such as stellar or disk mass, stellar accretion rate, and stellar multiplicity. Within the samples are interesting small minorities: transitional disks with sharp-edged, dust-free radial gaps or central clearings, and continuous disks that appear much like the majority except for a striking lack of crystalline or large dust grains. The former of these minorities strongly suggest the recent (~0.1 Myr) formation of giant planets within the disks. The latter, taken with the pattern of trends, variations and uncorrelations, suggests that giant-planet formation and subsequent Type II migration is an important modulation of disk evolution, a throttle that operates on time scales similar to the time scales for sedimentation, growth and thermal processing of dust. |