Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-02-25
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
2 pages, 1 figure. To be published in the proceedings of the conference "Why Galaxies Care about AGB Stars II", F. Kerschbaum,
Scientific paper
It is commonly believed that winds of cool giants in their late evolutionary stages are driven by radiative pressure on dust grains, but the actual grain species responsible for driving winds of M-type AGB stars are still a matter of debate (see H\"ofner, this volume). The optical properties of the dust particles responsible for initiating the outflow affect the stellar spectra in two ways: (i) indirectly, through their influence on the dynamical structure of the atmosphere/envelope and the resulting molecular features, and (ii) directly, by changes of the spectral energy distribution due to absorption and scattering on dust grains. The qualitative differences in the energy distributions of C-type and M-type AGB stars in the visual and near-infrared regions suggest that the dust particles in oxygen rich atmospheres are relatively transparent to radiation. By using detailed dynamical models of gas and radiation combined with a simple description for the dust opacity (which can be adjusted to mimic different wavelength dependencies and condensation temperatures) and also by adjusting the fraction of the opacity that is treated as true absorption, we investigate which dust properties produce synthetic photometry consistent with observations. The goal of this study is to narrow down the possible dust species that may be driving the winds in M-type AGB stars.
Aringer Bernhard
Bladh Sara
Hofner Susanne
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