Mass Loss from M Stars

Abstract

Infrared observations of M giants and supergiants show that circumstellar dust shells are frequently present. The observations permit the radii and densities of the dust shells to be determined. It is shown that radiation pressure drives the particles through the gas at a velocity that varies with the density. The momentum coupling drives the gas out of the star. Velocities of gas ejection are estimated and compared with optical and radio measures. Rates of mass ejection are calculated for a number of stars. These rates are compared with the rates required to maintain the interstellar medium at its present density.