Approximate lambdaoperators working at optimum convergence rate. II  Line transfer in expanding atmospheres
Abstract
An approximate lambdaoperator (ALO) developed for the line transfer problem in the comoving frame (CMF) is presented. The ALO is nearly identical to the exact diagonal of the linear term of the CMF lambda operator, and it provides a valuable tool for significantly accelerating the iteration of rate equations and radiative transfer. This local ALO is shown to be closely related to the corresponding quantity in the Sobolev approximation (SA), which will allow a new generation of nonLTE models of expanding atmospheres of hot luminous stars to be computed, as the CMF and the SA approach may be arbitrarily mixed. The possibility of mixing the different approaches will reduce the computing time significantly and allow a large number of elements different from H and He to be included in the unified treatment. The implementation of the ALO and the corresponding approximatelambdaiteration cycle in existing codes is straightforward and allows for the treatment of partial redistribution effects in the CMF and the incorporation of multiline effects quickly and effectively.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 August 1991
 Bibcode:
 1991A&A...248..581P
 Keywords:

 Computational Astrophysics;
 Convergence;
 Hot Stars;
 Nonequilibrium Thermodynamics;
 Operators (Mathematics);
 Radiative Transfer;
 Stellar Atmospheres;
 Equilibrium Equations;
 Iterative Solution;
 Line Spectra;
 Optical Thickness;
 Astrophysics