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Astron. Astrophys. 341, L47-L50 (1999)

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Letter to the Editor

Carbon molecules in the inner wind of the oxygen-rich Mira IK Tauri

Debiprosad Duari 1, Isabelle Cherchneff 1 and Karen Willacy 2

1 Department of Physics, UMIST, P.O. Box 88, Manchester, M60 1QD, UK
2 Jet Propulsion Laboratory, Pasadena, CA 91109, USA

Received 2 November 1998 / Accepted 17 November 1998

Abstract

The gas-phase non-equilibrium chemistry of the inner wind of the oxygen-rich Mira variable IK Tau (NML Tau) is investigated using a physio-chemical model describing the periodically shocked gas close to the stellar photosphere. We predict the formation in large amounts of a few carbon species in the inner envelope, in particular CO2, which has been recently detected with ISO in the spectra of several oxygen-rich semi-regular and Mira stars. The theoretical abundances are also in excellent agreement with values derived from millimeter and sub-millimeter observations, pointing to the fact that some carbon species in oxygen stars do form from shock chemistry in the inner layers and travel the envelope as "parent" species.

Key words: stars: abundances – stars: AGB and post-AGB – stars: circumstellar matter – stars: late-type

Send offprint requests to: dpd@saturn.phy.umist.ac.uk

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© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998
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