Dust Formation and Winds around Evolved Stars: The Good, the Bad and the Ugly Cases

S. Hoefner

Published 2009-03-30Version 1

Cool luminous giants, in particular asymptotic giant branch stars, are among the most important sources of cosmic dust. Their extended dynamical atmospheres are places where grains form and initiate outflows driven by radiation pressure, leading to considerable stellar mass loss and the enrichment of the interstellar medium with newly-produced elements. This review summarizes the current understanding of dust formation and winds in such stars, sketching a system of criteria for identifying crucial types of dust grains in the range of possible condensates. Starting with an overview of the specific conditions for dust formation in cool dynamic atmospheres, the role of grains as wind drivers, as well as their influence on observable properties of cool giants and the circumstellar environment is discussed in some detail. Regarding the literature, special attention is given to current developments, e.g., the debate concerning the Fe-content and size of silicate grains in M-type AGB stars which are critical issues for the wind mechanism, or recent advances in spatially resolved observations and 3D modeling of giants and their dusty envelopes.