Aperture synthesis studies of the chemical composition of protoplanetary disks and comets

Details Aperture synthesis studies of the chemical composition of protoplanetary disks and comets Aperture synthesis studies of the chemical composition of protoplanetary disks and comets

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt.........1q&link_type=abstract

Thesis (PhD). CALIFORNIA INSTITUTE OF TECHNOLOGY, Source DAI-B 62/05, p. 2353, Nov 2001, 141 pages.

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Scientific paper

There is an intimate connection between the solar nebula and the interstellar medium from which it formed. Improvements in observational methods have now made it possible to directly observe planet-forming environments around young stars and to better characterize the most primitive relics of planetary growth in our own solar system. This thesis describes one such method, aperture synthesis imaging using the Owens Valley Radio Observatory (OVRO) Millimeter Array, and its application to the chemical composition of circumstellar accretion disks and comets. The observations presented in this thesis concentrate on λ ~ 3 mm transitions of HCN/HCO+ and 13CO/CN in LkCa 15, GM Aur, MWC 480, and HD 163296. These disks were chosen based on their large spatial extent, Keplerian kinematic patterns, and strong CO emission. Two surround classical T Tauri stars and two encircle Herbig Ae stars, enabling the influence of the central stellar luminosity on the chemical composition of the disk to be investigated. All are well isolated from dense molecular clouds. The disk emission toward LkCa 15 is particularly intense, with many molecules being detected, including HCN/HCO+ and their 13C- isotopomers, DCN, CN, CH3OH, CS, SO, 13CO, and C18O. The overall abundance patterns are consistent with recent models of photon-dominated chemistry in the near surface regions of flaring circumstellar disks that also provide a natural explanation for the mid- and far-infrared properties of the disk spectral energy distribution. Finally, the detection of DCN has made possible the first determination of the critical D/H ratio in protoplanetary gas. At present, the data provides an approximate value of 0.01 for the DCN/HCN ratio, a value close to that found in the dark molecular clouds, but one that clearly arises from in situ disk chemistry. The OVRO Millimeter Array was able to image, for the first time, molecular analogs of the dust jets commonly observed at optical and infrared wavelengths. The production rates derived from the aperture synthesis images are similar to those found by other researchers, and reveal a marked similarity between the composition of Hale-Bopp and that derived for dense molecular clouds, in particular the hot cores observed near massive young stars. (Abstract shortened by UMI.)

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