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Astron. Astrophys. 357, 572-580 (2000)


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Dust formation in carbon-rich Wolf-Rayet stars *

I. Chemistry of small carbon clusters and silicon species

I. Cherchneff 1, Y.H. Le Teuff 1, P.M. Williams 2 and A.G.G.M. Tielens 3

1 Deparment of Physics, UMIST, P.O. Box 88, Manchester M60 1QD, UK
2 Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
3 Kapteyn Institute, University of Groningen, P.O. Box 800, 9700 Groningen, The Netherlands

Received 23 April 1998 / Accepted 25 August 1999

Abstract

The formation of small carbon chains and molecular precursors to silicon carbide grains is investigated in the hot, hostile environment of carbon-rich Wolf-Rayet (WC) winds. We consider only WC stars which produce dust on a continuous basis and develop for the first time non-equilibrium, chemical kinetic routes to nucleating dust precursors in the outflow. These can be used to calculate quantitatively the yield of such dust precursors for various outflow scenarios. Because WC stars have lost all their hydrogen in the WN phase, the chemical processes used in the model involve a pure helium, carbon, oxygen, silicon and sulphur chemistry which resembles that encountered in graphite or metal vaporization experiments in the laboratory. We derive abundances for small linear carbon clusters up to C6 and silicon-bearing species for various wind parameters and conclude that high-density regions in the form of clumps or discs are of paramount importance to the formation of dust in WC stars.

Key words: molecular data – molecular processes – stars: circumstellar matter – stars: Wolf-Rayet

* Appendix A is only available in electronic form at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/357/572 (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/357/572

Send offprint requests to: Y.H. Le Teuff

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000

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