Testing and Improving the Dynamical Theory of Mass Exchange

The study of the flow structure is of great importance, and the results can be used both for consideration of the evolution status of binary stars and for the interpretation of observational data. In this report we present the review of 3D gas dynamic models used for the description of the mass exchange in close binaries. Main features of the flow structure in steady-state close binaries are summarized. It is shown that in self-consistent considerations the interaction between the stream from the inner Lagrangian point and the forming accretion disc is shock-free, and, hence, a "hot spot" does not form at the outer edge of the disc. To explain the presence of the observed zones of high luminosity in close binaries a self-consistent "hot line" model was proposed according to which excess energy is released in a shock wave formed due to interaction between the circumdisc halo and the stream. The "hot line" model was confronted with observations and confirmed by virtue of comparison of synthetic and observational light curves for cataclysmic variables and by the analysis of Doppler tomograms. The special attention is paid at physics of accretion discs in binary systems and particularly at waves in discs. The possible observational manifestations of the "hot line" wave and two arms of the tidal shocks are discussed. We also suggest that an additional spiral density wave can exist in the inner parts of the cold accretion disc. This spiral wave is due to the retrograde precession of streamlines in the binary system. The results of 3D gas dynamic simulation have shown that a considerable increase in the accretion rate (by an order of magnitude) is associated with the formation of the ''precessional'' spiral wave. Basing on this fact we suggest a new mechanism for the superoutbursts and superhumps in close binaries.