Atmospheres and spectra of X-ray illuminated stars: A gray model

A gray model is used to explore the effect of heating of stellar atmospheres by an external X-ray flux. This flux is shown to produce additional heating functions in the surface and inner layers. The opacity sources in the X-ray region are determined. A technique for calculating the reflection effect in the gray approximation is presented. The illuminated and normal atmospheres and their spectra are shown to differ considerably