Book Description
"In this dissertation we investigate the characteristics of Class II protoplanetary disks in Orion A star-forming region. Our major goal is to analyze a large sample of protoplanetary disks with near- and mid-IR spectra, by statistical approaches, to understand protoplanetary disk evolution in Orion A. The topics with which we deal include the following: (1) Environmental and age effects on the evolution of protoplanetary disks; (2) Giant planet formation in the transitional disks of Orion A: a statistical study of correlations among disk and stellar properties; (3) The impact of extreme UV radiation on the protoplanetary disks near the Trapezium. For this work, 303 protoplanetary disks in Orion A region observed by IRS/Spitzer and the follow-up observation of 120 objects from SpeX/IRTF are used to reveal the characteristics of Class II disks in Orion A. For clues on environmental effects on disk evolution and planet formation, we compare the disk properties and dust properties of Orion A disks to that of Taurus disks and examine trends with respect to position within Orion A. We extract spectral indices, equivalent widths, and integrated fluxes from IRS spectra of Class II objects in Orion A which pertain to disk structure and dust composition. We measure mass accretion rates using hydrogen recombination lines in SpeX spectra of our targets. Utilizing the properties, we analyze the general distribution of properties of disks in ONC, L1641, and Taurus from their histograms. Our main findings are as follows: Transitional disks - those protoplanetary disks for which deficits of infrared excess signify sharp-edged gaps in the dust distribution - are produced gravitationally by companions to the central star. The vast majority of the companions (