A temperature correction method for expanding atmospheres
W.-R. Hamann and G. Gräfener
Model atmospheres form the basis for the interpretation of
stellar spectra. A major problem in those model calculations is to
establish the temperature stratification from the condition of radiative
equilibrium. Dealing with non-LTE models for spherically expanding
atmospheres of Wolf-Rayet stars, we developed a new temperature
correction method. Its basic idea dates back to 1955 when it was proposed
by Unsöld for grey, static and plane-parallel atmospheres in LTE. The
equations were later generalized to the non-grey case by Lucy. In the
present paper we furthermore drop the Eddington approximation, proceed
to spherical geometry and allow for expansion of the atmosphere. Finally
the concept of an "approximate lambda operator" is employed to speed
up the convergence. Tests for Wolf-Rayet type models demonstrate that the
method works fine even in situations of strong non-LTE.
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