AAS 205th Meeting, 9-13 January 2005
Session 140 Cold Gas and Molecular Clouds
Poster, Thursday, January 13, 2005, 9:20am-4:00pm, Exhibit Hall

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[140.08] Carbon Isotope Ratios in Molecular Clouds and Circumstellar Envelopes from Millimeter Observations of CN

S. N. Milam, L. M. Ziurys, N. J. Woolf (University of Arizona, Steward Observatory), S. Wyckoff (Arizona State University)

Observations of the N=1-0 and N=2-1 transitions of 12CN and its 13C isotopomer at 1.2 and 3 mm have been conducted towards both molecular clouds and the circumstellar envelopes of various types of stars, using the Kitt Peak 12 m antenna and the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory. These observations have been used to establish 12C/13C ratios in these objects. CN is particularly useful in this regard, because its spectra exhibit substantial hyperfine structure, from which accurate opacities can be evaluated. Ratios have been determined towards W31, G29.9, G19.6, G49.2, G35.2, S156, and WB391, with 12C/13C values of 20.5, 62.8, 70.5, 47.8, 94.8, 77.6, and 134.5. In conjunction with past CN observations of Savage et al. (2002, ApJ, 578, 211), these measurements suggest a 12C/13C gradient in the galaxy of 5.87DGC + 15.2. This gradient is close in value to that established from a grand average of these measurements, past CO and H2CO observations. Towards carbon-rich AGB and post AGB stars (e.g. IRC+10216, CRL618, CRL2688, and IRC+40540), measurements suggest preliminary 12C/13C isotope ratios in the range of 20-76. Observations are currently being conducted towards Hydrogen-deficient, Supergiants, Li-rich, and typical Carbon stars. Ratios established in these objects will also be reported.

This material is based upon work supported by the National Aeronautics and Space Administration through the NASA Astrobiology Institute under Cooperative Agreement No. CAN-02-OSS-02 issued through the Office of Space Science.

The author(s) of this abstract have provided an email address for comments about the abstract: lziurys@as.arizona.edu

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