DUST DRIVEN WINDS

The status of dust driven winds, constituting an important subclass of essentially radiation generated winds, is surveyed. Dust driven winds are conceived as a long lasting phenomenon of heavy mass loss concern ing those luminous cool giants and supergiants, where dust condensatio n in the expanding flow determines both the stellar mass loss late and the subsonic-supersonic transition of the velocity field. Our contrib ution aims at a self-consistent description of the dynamical shell str ucture with particular emphasis to the theoretical aspects of this imp ortant phenomenon. Thus, not only the complex coupling of the various ingredients (hydrodynamics, chemistry, radiative transfer, dust nuclea tion, and growth) is outlined in detail, but also general arguments re garding the overall structure of such winds and the expected position of their central objects in the Hertzsprung-Russel diagram are conduct ed. A selected typical self-consistent model for a stationary C-star s hell demonstrates the characteristic wind structure and gives insight into the close nonlinear interplay between dust formation and wind gen eration. During the late evolutionary stages of a star along the AGB d ust driven mass loss provides a natural self-accelerating mechanism wh ich easily can produce very high mass loss rates, an effect which poss ibly might play an important role for the Tip-AGB objects and the AGB- PN-transition.