Stochastic Methods for the Calculation of Mean Values of the Specific Intensities in Moving Late Type Atmospheres
Christian A. Graf (Institute of Theoretical Astrophysics)
Rainer Wehrse (Institute of Theoretical Astrophysics)
Cool stars show an extremely large number of atomic and molecular lines in their spectra. Unfortunately, in addition to the lines that are visible in spectra there are many more weak lines present that cannot be observed directly. They form a quasi-continuum. The question arises how these lines should be included in models. Since an individual treatment of all lines is very time-consuming, for static media several methods have been developed that result in specific intensities or fluxes that are averaged over a certain wavelength interval, e.g. methods involving opacity distribution functions or the opacity sampling method. Recently, Baschek et al. have proposed ways to generalize the opacity distribution functions to moving cases and to calculate them directly from a given line list or by means of a Poisson point process. After an introduction to these methods we present first results for the generalized opacity distribution function based on presently used line lists (assuming solar composition). We will discuss in particular its variation with the velocity gradient and demonstrate the changes in the effective absorption coefficient (that replaces the Rosseland mean absorption coefficient for static media) due to motions. Finally, we will address the problem of incomplete line lists and their consequences.