X-Ray Emission Region of a White Dwarf with Accretion

Abstract

As a model of X-ray stars of the Sco X-1 type the accretion of gas by a white dwarf is studied, and, in particular, the structure of a hot plasma formed by the accretion is examined in detail. It is found that the temperature distribution in the plasma is determined only by the mass of the star, while the density and the thickness of this plasma depend also on the accretion rate. Thus the relative spectrum of thermal X-rays emitted from the hot plasma is determined only by the stellar mass, while the luminosity changes proportionally to the accretion rate. This feature is supported by recent observations of Sco X-1 by Matsuoka et al. The mass of the white dwarf of Sco X-1 is estimated as 0.29M⊙.