Theoretical Color Mass-Loss Relations for O-Rich Mira Stars

Abstract

Mass-loss plays a key role for the stars on the Asymptotic Giant Branch (AGB), by dominating the subsequent evolution of the star (Olofsson 1999) and also, it is in this phase that low and intermediate mass stars contribute the most to the replenishment of the interstellar medium in the solar neighborhood (Sedlmayr 1994). It is therefore essential to estimate quantitatively the mass loss rates of AGB stars in the solar neighborhood and ideally, in different chemical environments such as the Bulge. Empirical correlations between IR color indices and mass loss rates have been found for Mira stars (Le Bertre & Winters 1998, hereafter LW98) which can provide an easy tool to measure directly their mass loss rates simply via infrared color indices, independent of the distance to the star. In this work, we present synthetic relations between infrared color indices and mass loss rates derived from time-dependent model calculations for circumstellar dust shells (CDS) around oxygen-rich AGB stars (Jeong et al. 2002, in preparation) and compare these relations to the empirical relations in LW98