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


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Dust cloud formation in stellar environments

I. A radiative/thermal instability of dust forming gases

P. Woitke 1, E. Sedlmayr 1 and B. Lopez 2

1 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 [FORMULA] and show that, in the linear approximation, the mean intensity [FORMULA] 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 ([FORMULA]), 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)

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000

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