Astron. Astrophys. 330, 676-684 (1998)

Silicon and sulphur chemistry in the inner wind of IRC+10216 ^*

Karen Willacy and Isabelle Cherchneff

Department of Physics, UMIST, P.O. Box 88, Manchester M60 1QD, UK

Received 5 June 1997 / Accepted 22 August 1997

Abstract

We present a dynamical and chemical model of the inner wind of the carbon-rich, AGB star IRC+10216. We include the effect of pulsation-driven shocks on the gas envelope close to the stellar photosphere and construct an extended chemical model that includes in particular the chemistry of hydrocarbon species and silicon and sulphur-bearing molecules. The derived theoretical abundances for many molecules are in excellent agreement with values obtained from observations of infrared ro-vibrational molecular lines. We confirm the "parent" character of certain chemical species and show that the inner wind of IRC+10216, and more generally of evolved AGB stars, is an active dynamical and chemical region where molecules are formed and processed.

Key words: molecular processes stars: AGB stars: individual: IRC+10216

* Table 5 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: I. Cherchneff

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Contents

• 1. Introduction
• 2. The model
  • 2.1. Dynamics
  • 2.2. Chemistry
• 3. Results
  • 3.1. Atomic and molecular hydrogen
  • 3.2. Silicon and sulphur species
  • 3.3. CH₄, NH₃ and SiH₄
  • 3.4. Oxygen-bearing molecules
  • 3.5. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998
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