Dust-driven winds and mass loss of C-rich AGB stars with subsolar metallicities

¹ Zentrum für Astronomie und Astrophysik (ZAA), Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany e-mail: awachter@physik.tu-berlin.de
² Department of Physics and Astronomy, Division of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden
³ Institut de RadioAstronomie Millimétrique (IRAM), 300 rue de la Piscine, Domaine Universitaire, 38406 Saint-Martin d'Hères, France
⁴ Departamento de Astronomia de la Universidad de Guanajuato, Apartado Postal 144, C.P. 36000, Guanajuato, GTO, Mexico

Received: 2 April 2008
Accepted: 21 May 2008

Abstract

Aims. We investigate the mass loss of highly evolved, low- and intermediate mass stars and stellar samples with subsolar metallicity. We give a qualitative as well as quantitative description which can be applied to LMC/SMC-type stellar populations.

Methods. For that purpose we apply the same approach as we did for solar metallicity stars and calculate hydrodynamical wind models including dust formation with LMC and SMC abundances under consideration of an adapted model assumption. In particular, we improved the treatment of the radiative transfer problem in order to accommodate larger non-local contributions occurring with smaller opacities. For each wind model we determine an averaged mass-loss rate. The resulting, approximate mass-loss formulae are then applied to well-tested and calibrated stellar evolution calculations in order to quantify the stellar mass loss.

Results. The dynamical models for LMC and SMC metallicity result in mass-loss rates of the same order of magnitude as the solar metallicity models which is in this basic approach in agreement with observations. The hydrodynamical properties like e.g. the outflow velocity differ (for fixed C/O abundance ratio) noticeably, though. While critical luminosities of LMC and solar metallicity models fairly coincide, the SMC models need higher luminosities to develop dust-driven winds.