Dynamic model atmospheres of AGB stars
IV. A comparison of synthetic carbon star spectra with observations

R. Gautschy-Loidl, S. Höfner, U.G. Jørgensen, J. Hron

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 micrometers 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 micrometers. At longer wavelengths our models showing mass loss offer a first self-consistent qualitative explanation of why a strong feature around 14 micrometers, which is predicted by all hydrostatic models as well as dynamical models showing no mass loss, is missing in observed AGB carbon star spectra.

A&A, in press