A Steady State Model of X-Ray Emitting Coronae around Accreting Non-Magnetic White Dwarfs in Cataclysmic Variables

Abstract

The X-ray emission of non-magnetic cataclysmic variable stars is considered. It is well known that a nearly spherical hot corona is produced around accreting white dwarfs because of strong viscous heating, and of rather inefficient cooling of matter at the boundary layer if the accretion rate is below some critical value. A steady state model of X-ray emitting coronae, into which mass is steadily supplied from the boundary layer, is then constructed and the X-ray spectra are calculated as functions of the mass-supply rate Ṁs. Eclipses of such corona were simulated. It has been found that the thermal energy of the corona is transported downward by conduction to the denser area near to the surface of the white dwarf, where it is emitted as X-ray radiation. Around 5% of the matter supplied by the disk could leave the system as stellar wind. Most of the X-rays are radiated from regions near to the white dwarf surface within this model. Eclipse simulations of this model agree with recent observations of eclipsing system HT Cas.