University of Missouri - Saint Louis
The Graduate School
An oral examination in defense of the dissertation for the degree
Doctor of Philosophy in Physics
Kari Anne Wojtkowski
M.S. in Physics, May, 2001, University of Missouri-St. Louis.
B.S. in Physics, May, 1999, University of Missouri-Rolla.
The Characterization of Volatiles Associated with Young Stellar Objects
In the first portion of this work, we searched for differences in volatiles within a single star forming region, Rho Ophiuchi. We determined the amount, temperature, and composition of two ice features, the bending modes of CO2 and H2O at 15 μm and 6 μm, respectively, toward 28 YSOs. We found that more than 50% of the YSOs studied contained a portion of crystalline CO2 ice. We also found that some sources with Flat or borderline Class II Spectral Energy Distributions (SEDs) have a larger abundance of CO2 ice with respect to H2O ice. In addition to intracloud differences, we compared our results with several other star forming regions, high mass YSOs, and background objects. The average abundance of CO2 with respect to H2O in Rho Oph is comparable to that in Taurus, Perseus, and the value reported by Oberg et al. (2011) toward high mass YSOs, however, it is less than the average abundance reported toward Corona Australis, Serpens, and the value cited by Oberg et al. (2011) toward low mass YSOs. The second half of this work involved a study of gaseous HCN, C2H2, and CO toward a nearly edge-on low mass binary system, GV Tau. We report the second detection of these simple molecules toward a low mass YSO. The abundances of these molecules agree with that toward the first low mass YSO with a detection, IRS 46 Lahuis et al. (2006), the Markwick et al. (2002) models and comets. We also found that these molecules have a rotational temperature of !100 K - 200 K, indicating they may be located in the warm molecular layer of the disk. This work is part of a larger study to characterize volatiles (others include CH4, NH3, the 6.8 μm absorption feature, and CH3OH) in the gas and/or solid phase toward YSOs in different star forming regions. This characterization includes temperature, location, mass, evolutionary state, and abundance. These characteristics will be used as a diagnostic tool to determine the evolution of molecules during the star formation process.
|Date: July 31, 2012||
Time: 2:00 p.m. to 4:00 p.m.
Place: 102 SCB
Erika Gibb, Ph.D. (Co-Advisor)
|John Schmitt, Ph.D. (Co-Advisor)|
|Bruce Wilking, Ph.D.||Jerry Peacher, Ph.D.|
|Terry Rettig, Ph.D.|