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Astron. Astrophys. 349, 243-252 (1999)


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Optical properties of carbon grains: Influence on dynamical models of AGB stars

Anja C. Andersen 1, Rita Loidl 2 and Susanne Höfner 2,3

1 Niels Bohr Institute, Astronomical Observatory, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark (anja@astro.ku.dk)
2 Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, A-1180 Vienna, Austria (loidl@astro.univie.ac.at)
3 Uppsala Astronomical Observatory, Box 515, S-75120 Uppsala, Sweden (hoefner@astro.uu.se)

Received 14 April 1999 / Accepted 7 July 1999

Abstract

For amorphous carbon several laboratory extinction data are available, which show quite a wide range of differences due to the structural complexity of this material. We have calculated self-consistent dynamic models of circumstellar dust-shells around carbon-rich asymptotic giant branch stars, based on a number of these data sets. The structure and the wind properties of the dynamical models are directly influenced by the different types of amorphous carbon. In our test models the mass loss is not severely dependent on the difference in the optical properties of the dust, but the influence on the degree of condensation and the final outflow velocity is considerable. Furthermore, the spectral energy distributions and colours resulting from the different data show a much wider spread than the variations within the models due to the variability of the star. Silicon carbide was also considered in the radiative transfer calculations to test its influence on the spectral energy distribution.

Key words: hydrodynamics – radiative transfer – stars: atmospheres – stars: carbon – stars: AGB and post-AGB

Send offprint requests to: A.C. Andersen

© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999

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