Pulsation and Stellar Winds: Some Lessons Learned from Dynamical Models of the Atmospheres of Cool Stars

Abstract

Stellar pulsation is associated with some of the most dramatic epochs of mass loss from stars. Detailed numerical modeling calculations that reproduce the observed characteristics of such mass losing stars necessarily include a number of key physical processes. The reader is referred to detailed calculations of dynamical atmospheres for Mira variables (Bowen 1988 (=B88) and 1998 (=B98)). A review of physical processes with examples from a variety of computations for Miras, Cepheids, and RR Lyrae stars is given by Willson, Struck & Bowen (1997 = WSB), and evolutionary consequences are outlined by Willson, Bowen Si Struck (1996 = WBS). This review focusses on (1) the importance of departures from LTE, radiative equilibrium, and chemical equilibrium and (2) the treatment of “piston” boundary conditions. We then compare the results of different modeling calculations with observed Mira period-luminosity relations. Finally, we summarize the implications for “cyclical variations” in stellar winds.