Astron. Astrophys. 358, 665-670 (2000)

Dust cloud formation in stellar environments

I. A radiative/thermal instability of dust forming gases

P. Woitke ¹, E. Sedlmayr ¹ and B. Lopez <sup>2

1</sup> TU Berlin, Institut für Astronomie und Astrophysik, Sekr. PN 8-1, Hardenbergstrasse 36, 10623 Berlin, Germany
² Observatoire de la Côte d'Azur, Département Fresnel UMR 6528, B.P. 4229, 06034 Nice Cedex 4, France

Received 24 February 2000 / Accepted 13 April 2000

Abstract

In this paper, we report on an instability possibly inherent in dust forming media due to multi-dimensional radiative transfer effects. Starting from a solution of a grey 1D or 2D radiative transfer problem, we introduce small harmonic 3D-perturbations of the opacity structure and show that, in the linear approximation, the mean intensity is modified in the same manner, resulting in spatial variations of the temperature structure. If the medium possesses a strongly temperature-dependent opacity - as expected in dust forming environments - the perturbations can be self-amplifying. We apply this concept to a spherically symmetric, stationary model for the dust-driven wind of IRC+10216 and find that large-scale perturbation modes perpendicular to the radial direction are unstable in the outer parts of the dust formation region (), which may result in the formation of dust clouds.

Key words: instabilities radiative transfer ISM: dust, extinction stars: late-type stars: circumstellar matter stars: individual: IRC+10216

Send offprint requests to: P. Woitke (woitke@physik.tu-berlin.de)

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Contents

• 1. Introduction
• 2. The nature of the instability
• 3. Radiative transfer in a perturbed medium
  • 3.1. Basic form of the radiative transfer equation
  • 3.2. Consideration of perturbations
• 4. Results
• 5. Discussion
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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