Blake, Geoffrey A. (2003) Chemistry in Circumstellar Disks as Probed by High Resolution Millimeter-Wave to Infrared Spectroscopy. In: Chemistry as a Diagnostic of Star Formation. NRC Research Press , Ottawa, pp. 178-187. ISBN 0-660-19089-3 http://resolver.caltech.edu/CaltechAUTHORS:20121022-083707400
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The role of high spectral and spatial resolution spectroscopy in understanding the evolution of the gaseous component of the circumstellar accretion disks encircling low mass stars is described. Millimeter-wave emission lines from trace constituents such as CO, CN, HCO^+, and HCN can be used to probe the kinematic and physiochemical properties in the near-surface regions of disks beyond 100AU, but, thanks to extensive molecular depletion in the midplane, they are not a reliable proxy for the disk mass. Future observations of the pivotal deuterated species HD and the molecular ion H_2D^+ may provide more robust access to the outer disk midplane. In the critical planet-forming region from 1 to 30 AU, mid-infrared observations of the pure rotational transitions of molecular hydrogen would alleviate many of the concerns raised by the (sub)millimeter spectral line observations, and results from the ISO-SWS instrument on several "transitional" disks are presented. The measurements of these weak lines used beams substantially larger than the disk angular diameter, and so must be verified or refuted by high angular resolution spectroscopy from the ground. Finally, the high-resolution M-band (5 µm) spectroscopy of CO in disks is outlined. Emission lines that are likely optically pumped by hot dust in the inner disk (R ≾ 1 AU) are seen toward inclined systems, while the absorption spectra of edge-on disks clearly reveal the molecular depletion inferred at millimeter wavelengths. A wide variety of molecules can be studied with high-resolution spectroscopy in the near-to mid-infrared, and such observations would permit the first direct comparison of cometary and circumstellar ices.
|Item Type:||Book Section|
|Additional Information:||© 2003 NRC Research Press. The results outlined here form the thesis and postdoctoral research of several young scientists at Caltech and in Prof. Ewine van Dishoeck's astrochemistry group at Leiden University with whom it has been my great privilege to learn these several years. Their dedication and camaraderie are gratefully acknowledged. The OVRO Millimeter Array and Caltech Submillimeter Observatory are operated with support from the National Science Foundation AST 99-81546 and AST 99-80846. The NIRSPEC were obtained at the Keck II telescope of the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.|
|Subject Keywords:||astrochemistry; infrared : ISM; ISM : molecules; planetary systems : protoplanetary disks; stars : formation|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||22 Oct 2012 17:01|
|Last Modified:||22 Oct 2012 17:01|
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