Atmospheric dynamics in carbon-rich Miras

II. Models meet observations

¹ Institut für Astronomie der Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria e-mail: nowotny@astro.univie.ac.at
² Departement of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden

Received: 17 December 2005
Accepted: 28 February 2005

Abstract

Originating in different depths of the very extended atmospheres of AGB stars, various molecular spectral lines observable in the near-infrared show diverse behaviours and can be used to probe atmospheric dynamics throughout the outer layers of these pulsating red giants. In Nowotny et al. (2005b, A&A, 437, 273, Paper I) time series of synthetic high-resolution spectra were presented, computed from a dynamic model atmosphere for a typical carbon-rich Mira. In this work, line profile shapes, their variations during the lightcycle and radial velocities derived from wavelength shifts are analyzed and compared with results from observed FTS spectra of the C-rich Mira S Cep and other Miras. It is found that the global velocity structure of the model is in qualitative agreement with observations. Radial velocities of molecular lines sampling different layers behave comparably, although some differences are apparant concerning absolute values. A correction factor of between measured RVs and actual gas velocities is derived for CO lines. It is shown that dynamic model atmospheres are capable of reproducing Mira spectra without introducing an additional “static layer” proposed by several authors.