Optical properties of carbon grains: Influence on dynamical models of AGB stars

For amorphous carbon several laboratory extinction data are available, whic h show quite a wide range of differences due to the structural complexity o f this material. We have calculated self-consistent dynamic models of circu mstellar dust-shells around carbon-rich asymptotic giant branch stars, base d on a number of these data sets. The structure and the wind properties of the dynamical models are directly influenced by the different types of amor phous carbon. In our test models the mass loss is not severely dependent on the difference in the optical properties of the dust, but the influence on the degree of condensation and the final outflow velocity is considerable. Furthermore, the spectral energy distributions and colours resulting from the different data show a much wider spread than the variations within the models due to the variability of the star. Silicon carbide was also conside red in the radiative transfer calculations to test its influence on the spe ctral energy distribution.