Dust formation in winds of long-period variables
IV. Atmospheric dynamics and mass loss

S. Höfner and E.A. Dorfi

We have calculated radiation-hydrodynamical models of the atmosphere and circumstellar dust shell of C-rich long-period variables which include a detailed description of the dust formation process. We discuss the time-dependent behaviour of the circumstellar envelope (e.g. multiperiodicity) and its relevance for observational properties like near-IR light curves and investigate the time-averaged mass loss characteristics of a sample of models satisfying radius--luminosity--mass and period--luminosity relations. The results can be summarized as follows: The dependence of the mass loss rate on stellar parameters predicts a strong increase of mass loss as stars evolve along the AGB. The models presented agree reasonably well with mean mass loss--period relations deduced from observations of Mira stars and the observed scatter of mass loss rates for a given period can be understood in terms of pulsation amplitude or non-linearities of the wind mechanism. The wind velocities show a good correlation with a quantity which characterizes the strength of radiation pressure on dust relative to gravitation.

A&A 319, 648