Three-dimensional numerical simulation of gaseous flow structure in semidetached binaries

The results of numerical simulation of mass transfer in semidetached non-magnetic binaries are presented. We, investigate the morphology of gaseous flows on the basis of three-dimensional gas-dynamical calculations of interacting binaries of different types (cataclysmic variables and low-mass X-ray binaries). We find that taking into account a circumbinary envelope leads to significant changes in the stream-disc morphology. In particular, the obtained steady-state self-consistent solutions show an absence of impact between the gas stream from the inner Lagrangian point L-1 and the forming accretion disc. The stream deviates under the action of the gas of the circumbinary envelope, and does not cause the shock perturbation of the disc boundary (traditional hotspot). At the same time, the gas of the circumbinary envelope interacts with the stream and causes the formation of an extended shock wave, located on the stream edge. We discuss the implication of this model without hotspot (but with a shock wave located outside the disc) for interpretation of the observations. The comparison of synthetic light curves with observations proves the validity of the discussed gas-dynamical model without hotspot. We have also considered the influence of the circumbinary envelope on the mass transfer rate in semidetached binaries. The obtained features of flow structure in the vicinity of L-1 show that the gas of the circumbinary envelope plays an important role in the flow dynamics, and that it leads to significant (in order of magnitude) increase of the mass transfer rate. The most important contribution to this increase is from the stripping of the mass-losing star atmosphere by interstellar gas flows, The parameters of the formed accretion disc are also given in the paper. We discuss the details of the obtained gaseous flow structure for different boundary conditions on the surface of mass-losing star, and show that the main features of this structure in semidetached binaries are the same for different cases. The comparison of gaseous flow structure obtained in two- and three-dimensional approaches is presented. We discuss the common features of the how structures and the possible reasons for revealed differences.