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Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 2009.
I present an analysis of mid-infrared spectra of T Tauri stars observed largely as part of
the Spitzer IRS Disks Guaranteed Time Observing program, focusing on the composition
of the solid-state dust in the upper layers of the protoplanetary disks surrounding
these stars. First, I quickly summarize our understanding of the early evolution of
our Solar System, with special regard to studies of primitive Solar System dust, and
I review studies of Young Stellar Objects. I describe how the data are reduced via
spectral extraction methods designed to yield high quality spectra. Next, I provide
some background on radiative transfer models of protoplanetary disks to justify the
use of simplified dust emission models to measure the dust composition of the upper
layers of these disks. I apply these models to five protoplanetary disk spectra that
each show evidence for a high abundance of silica dust, in order to identify the polymorphs,
or crystalline forms, of silica most likely giving rise to the distinctive features
in the spectra, and I discuss the implications for processing of dust in protoplanetary
disks. This is followed by a discussion on finding the optimal dust grain opacities to
use in modeling protoplanetary disks and some limitations of the simple dust emission
models I use. Finally, I discuss dust emission models fit to spectra of sixty-five Class II
Young Stellar Objects in the Taurus-Auriga star-forming region and the implications
for grain growth, dust processing, and protoplanetary disk evolution.
