NonLTE Lineblanketed Model Atmospheres of Hot Stars. I. Hybrid Complete Linearization/Accelerated Lambda Iteration Method
Abstract
A new munerical method for computing nonLocal Thermodynamic Equilibrium (nonLTE) model stellar atmospheres is presented. The method, called the hybird complete linearization/accelerated lambda iretation (CL/ALI) method, combines advantages of both its constituents. Its rate of convergence is virtually as high as for the standard CL method, while the computer time per iteration is almost as low as for the standard ALI method. The method is formulated as the standard complete lineariation, the only difference being that the radiation intensity at selected frequency points is not explicity linearized; instead, it is treated by means of the ALI approach. The scheme offers a wide spectrum of options, ranging from the full CL to the full ALI method. We demonstrate that the method works optimally if the majority of frequency points are treated in the ALI mode, while the radiation intensity at a few (typically two to 30) frequency points is explicity linearized. We show how this method can be applied to calculate metal lineblanketed nonLTE model atmospheres, by using the idea of 'superlevels' and 'superlines' introduced originally by Anderson (1989). We calculate several illustrative models taking into accont several tens of thosands of lines of Fe III to Fe IV and show that the hybrid CL/ALI method provides a robust method for calculating nonLTE lineblanketed model atmospheres for a wide range of stellar parameters. The results for individual stellar types will be presented in subsequent papers in this series.
 Publication:

The Astrophysical Journal
 Pub Date:
 February 1995
 DOI:
 10.1086/175226
 Bibcode:
 1995ApJ...439..875H
 Keywords:

 Hot Stars;
 Iterative Solution;
 Numerical Analysis;
 Radiative Transfer;
 Stellar Atmospheres;
 Stellar Models;
 Absorptivity;
 Equilibrium Equations;
 Jacobi Matrix Method;
 Line Spectra;
 Linearization;
 NewtonRaphson Method;
 Astrophysics;
 METHODS: NUMERICAL;
 RADIATIVE TRANSFER;
 STARS: ATMOSPHERES;
 STARS: EARLYTYPE