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Astron. Astrophys. 342, 531-541 (1999)

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Dynamic model atmospheres of AGB stars

II. Synthetic near infrared spectra of carbon stars

R. Loidl 1, S. Höfner 2, U.G. Jorgensen 2 and B. Aringer 1

1 Institut für Astronomie der Universität Wien, Türkenschanzstrasse 17, A-1180 Wien, Austria
2 Niels Bohr Institute, Astronomical Observatory, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark

Received 25 August 1998 / Accepted 17 November 1998


We have calculated synthetic opacity sampling spectra for carbon-rich Asymptotic Giant Branch (AGB) stars based on dynamic model atmospheres presented in the first paper of this series. We discuss how different model parameters influence the resulting synthetic spectra and how the spectra vary with phase. The molecules included are: CO, CH, CN, C2, HCN, C2H2 and C3. We show in which atmospheric layers the different molecules form, in an attempt to understand the qualitatively different variation with pulsation phase exhibited by various spectral features. Almost all features are blends of transitions from more than one molecule, and we therefore identify the most important transitions and molecules that contribute to the main spectral features from 0.5 to 12 µm. Furthermore, we demonstrate the effect on the individual spectral features due to the carbon depletion when dust is formed in the atmosphere.

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

Send offprint requests to: R. Loidl (loidl@astro.univie.ac.at)

© European Southern Observatory (ESO) 1999

Online publication: February 22, 1999