Envelopes of cool giant stars: a hybrid model.

A hybrid mechanism is proposed for consideration of mass loss from cool giant stars which involves chromosphere evaporation and radiation pressure on molecules. Emphasis is given to the differences between purely radiative winds and the present model, and average chromospheric temperatures are estimated which are compatible with the previously determined mass loss rate. The model geometry assumes a hybrid envelope consisting of a warm chromosphere above the stellar photosphere, surrounded by a cool layer which contains atomic gas and molecules. It is further assumed that the chromosphere is optically thin and isothermal.