Model atmospheres of near-Eddington limit X-ray bursters

Abstract

Some very simple, plane-parallel models of atmospheres of X-ray bursters that are very close to the Eddington limit are presented. The dominant opacity source is assumed to be incoherent Thomson scattering. Free-free transitions are responsible for the creation of soft photons. At large optical depths, there is LTE, while at small optical depths, electron scattering is coherent. The bulk of the radiative flux at intermediate optical depths is described by a Wien distribution with a chemical potential that varies with optical depth. Models with luminosities up to L = 0.9999L(E) are developed. At higher luminosities, it is necessary to allow for the sphericity of the extended, radiation pressure dominated atmospheres. The spectral (i.e. color) temperature in the extreme models is more than twice the effective temperature. Spectra obtained agree well with those calculated by London et al. (1986), with a much more sophisticated computer program. 19 references.