Dynamic model atmospheres of AGB stars

III. Effects of frequency-dependent radiative transfer

¹ Dept. of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden
² Rüti, Switzerland e-mail: rita@gautschy.ch
³ Niels Bohr Institute, Astronomical Observatory, Juliane Maries Vej 30, 2100 Copenhagen, Denmark

Corresponding author: S. Höfner, hoefner@astro.uu.se

Received: 26 June 2002
Accepted: 26 November 2002

Abstract

We present a new generation of model atmospheres for AGB stars which combine time-dependent dynamics and frequency-dependent radiative transfer. This allows us to take both the effects of pulsation (shock waves, stellar winds) and the complex influence of molecular opacities into account. In the case of C-rich stars, the models also include a self-consistent time-dependent description of dust formation. We investigate the influence of frequency-dependent radiative transfer on the energy and momentum balance of the atmosphere and compare our new models to existing grey dynamical models as well as to classical hydrostatic model atmospheres. We stress the importance of non–grey radiative transfer for obtaining realistic density–temperature structures even in highly dynamical models, discussing both the resulting observable properties and the wind characteristics. Presenting synthetic spectra, we argue that the current dynamical models represent an important step in a process leading from a qualitative to a quantitative description of atmospheres and winds of pulsating AGB stars.