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J.E. Kessler-Silacci (UT)
As analogs to the solar nebula, circumstellar disks offer a unique opportunity to study the conditions during the star and planet formation process. In this study, several millimeter-wave molecular lines were observed toward a sample of disks encircling T Tauri and Herbig Ae stars with the Owens Valley Millimeter Array in order to quantitatively examine the chemistry of the biogenic elements (C, N, O, S) in accretion disks. Toward this goal, existing radiative transfer models were modified for direct comparison with the observations to aid in the interpretation of molecular line emission and comparison with the predictions of chemical models. A survey of CN, HCN, CO and HCO+ in 7 Herbig Ae and T Tauri star disks was performed in order to probe the effects of UV fields on disk chemistry; CN and HCO+ are found to be sensitive to the strength of the local UV field. The first interferometric studies of deuterium in disks were performed and HDO and DCN were detected toward the T Tauri disk LkCa 15 and the Herbig Ae disk HD 163296. The deuterium enrichments are similar to that of molecular clouds, hot cores, and comets, consistent with comet formation in the outer regions of disks. The distribution of HDO in LkCa 15 was found to be similar to predictions from chemical models, which suggest a steep gradient as a function of disk radius. Finally, Keck LWS observations of the 8-13 micron silicate emission feature toward several T Tauri and Herbig Ae stars at various stages of the star formation process indicated an evolutionary trend similar to that previously seen with ISO for disk s around intermediate mass stars. However, emission from crystalline silicates was only detected toward one low mass star, Hen 3-600A, possibly indicating that crystallization processes occur less frequently, or are more difficult to observe at mid-infrared wavelengths, in these disks.
This work was supported by the NASA Graduate Student Researchers Program, NGT5-50231, and the National Science Foundation, grant No. 9981546.
The author(s) of this abstract have provided an email address for comments about the abstract: jes@astro.as.utexas.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.