Mass-Loss Rates of MS and S Stars Compared with their Infrared Photometry

The Asymptotic Giant Branch (AGB) phase marks the end of the evolution of low- and intermediate-mass stars, which are fundamental contributors to the mass-return to the interstellar medium and to the chemical evolution of galaxies. The detailed understanding of mass-loss processes is hampered by poor knowledge of the luminosities and distances of AGB stars. This contribution is focused on the study of the mass-loss rates for a sample of Galactic S stars. The properties of the stellar winds are re-analyzed with reliable estimates of distance on the basis of criteria determined in previous works. Stellar winds in S stars are on average less efficient than those of C-rich AGB stars of the same luminosity. Infrared colors appear to be crucial in this study. They show a good correlation with mass-loss rates for the Mira stars. This relation between the mass-loss rates of the stellar winds and infrared colors improves our understanding of the late evolutionary stages of low-mass stars and could be the origin of the correlation between mass-loss rates of the stellar winds and bolometric magnitudes.