Statistical equilibrium calculations for silicon in earlytype model stellar atmospheres
Abstract
Line profiles of 36 multiplets of silicon (Si) II, III, and IV were computed for a grid of model atmospheres covering the range from 15,000 to 35,000 K in effective temperature and 2.5 to 4.5 in log (gravity). The computations involved simultaneous solution of the steadystate statistical equilibrium equations for the populations and of the equation of radiative transfer in the lines. The variables were linearized, and successive corrections were computed until a minimal accuracy of 1/1000 in the line intensities was reached. The common assumption of local thermodynamic equilibrium (LTE) was dropped. The model atmospheres used also were computed by nonLTE methods. Some effects that were incorporated into the calculations were the depression of the continuum by free electrons, hydrogen and ionized helium line blocking, and autoionization and dielectronic recombination, which later were found to be insignificant. Use of radiation damping and detailed electron (quadratic Stark) damping constants had small but significant effects on the strong resonance lines of Si III and IV. For weak and intermediatestrength lines, large differences with respect to LTE computations, the results of which are also presented, were found in line shapes and strengths. For the strong lines the differences are generally small, except for the models at the hot, lowgravity extreme of our range. These computations should be useful in the interpretation of the spectra of stars in the spectral range B0B5, luminosity classes III, IV, and V.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 February 1976
 Bibcode:
 1976STIN...7618009K
 Keywords:

 Equilibrium Equations;
 Line Spectra;
 Silicon;
 Stellar Atmospheres;
 Spectrum Analysis;
 Tables (Data);
 Thermodynamic Equilibrium;
 Astronomy