Hypothetical scheme of the W Vir atmosphere and envelope. Two shocks are indicated: the main shock that amounts in the atmosphere, and the secondary shock which is falling on the star. The absorption components of the hydrogen line located at zero speed (N4 component, see Fig. 13 for designations), and redshifted (N2 component) are expected to be formed within the envelope and the upper atmosphere, respectively. The UV flux comes mainly from nearby hot stars of W Virginis.