Dust driven mass loss from carbon stars as a function of stellar parameters - I. A grid of Solar-metallicity wind models

Details Dust driven mass loss from carbon stars as a function of stellar parameters - I. A grid of Solar-metallicity wind models Dust driven mass loss from carbon stars as a function of stellar parameters - I. A grid of Solar-metallicity wind models

2009-09-08

arxiv.org/abs/0909.1513v2

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

27 pages, 11 figures, to appear in Astronomy & Astrophysics. Corrections by language editor included in this new version

Scientific paper

10.1051/0004-6361/200912084

[Abridged] We have computed a grid of 900 numeric dynamic model atmospheres (DMAs) using a well-tested computer code. This grid of models covers most of the expected combinations of stellar parameters, which are made up of the stellar temperature, the stellar luminosity, the stellar mass, the abundance of condensible carbon, and the velocity amplitude of the pulsation. The resultant mass-loss rates and wind speeds are clearly affected by the choice of stellar temperature, mass, luminosity and the abundance of available carbon. In certain parts of the parameter space there is also an inevitable mass-loss threshold, below which a dust-driven wind is not possible. Contrary to some previous studies, we find a strong dependence on the abundance of free carbon, which turns out to be a critical parameter. Furthermore, we have found that the dust grains that form in the atmosphere may grow too large for the commonly used small particle approximation of the dust opacity to be strictly valid. This may have some bearing on the wind properties, although further study of this problem is needed before quantitative conclusions can be drawn. The wind properties show relatively simple dependences on stellar parameters above the mass-loss threshold, while the threshold itself is of a more complicated nature. Hence, we chose not to derive any simplistic mass-loss formula, but rather provide a mass-loss prescription in the form of an easy-to-use FORTRAN routine. Since this mass-loss routine is based on data coming from an essentially self-consistent model of mass loss, it may therefore serve as a better mass-loss prescription for stellar evolution calculations than empirical formulae. Furthermore, we conclude that there are still some issues that need to be investigated, such as the role of grain-sizes.

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