Dynamic model atmospheres of AGB stars

IV. A comparison of synthetic carbon star spectra with observations

¹ Froburgstrasse 43, 4052 Basel, Switzerland
² Dept. of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden
³ NORDITA, Blegdamsvej 17, 2100 Copenhagen, Denmark
⁴ Niels Bohr Institute, Astronomical Observatory, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁵ Institut für Astronomie der Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria

Corresponding author: R. Gautschy-Loidl, rita@gautschy.ch

Received: 13 December 2003
Accepted: 8 April 2004

Abstract

We have calculated synthetic opacity sampling spectra for carbon-rich Asymptotic Giant Branch (AGB) stars based on dynamic model atmospheres which couple time-dependent dynamics and frequency-dependent radiative transfer, as presented in the third paper of this series. We include the molecules CO, CH, CN, C₂, CS, HCN, C₂H₂ and C₃ in our calculations, both when computing the atmospheric structures, and the synthetic spectra. A comparison of the synthetic spectra with various observed colours and spectra in the wavelength range between 0.5 and 25 μm of TX Psc, WZ Cas, V460 Cyg, T Lyr and S Cep is presented. We obtain good agreement between observations gathered at different phases and synthetic spectra of one single hydrodynamical model for each star in the wavelength region between 0.5 and 5 μm. At longer wavelengths our models showing mass loss offer a first self-consistent qualitative explanation of why a strong feature around 14 μm, which is predicted by all hydrostatic models as well as dynamical models showing no mass loss, is missing in observed AGB carbon star spectra.