MHD Modeling of Mass Transfer Processes in Close Binary Stars

Abstract

A three-dimensional numerical model has been developed to study the flow structure in close binary systems with a magnetic field. The model uses a system of equations of modified magnetic hydrodynamics, which allows describing all the main dynamic effects associated with the magnetic field. It takes into account the processes of radiation heating and cooling, heating due to current dissipation, as well as magnetic field diffusion. The model allows calculations in a wide range of magnetic field values. Comparison of the calculation results with observational data confirms the reliability and high efficiency of the model. The paper presents the calculation results of the flow structure in a typical intermediate polar. It is shown that an accretion disk is formed in such a binary system, which has the following characteristic features: “hot line”, tidal shock waves, precession density wave, magnetospheric region, and accretion columns. In this case, the magnetic field in the disk is predominantly toroidal. The paper also presents the results of calculations for typical polars. In such systems, instead of an accretion disk, a collimated stream of matter is formed, moving along the magnetic field lines to the magnetic poles of the white dwarf. It is shown that in synchronous polars, variations of the mass transfer rate lead to a change in the spatial configuration of the flow. In asynchronous polars, changes in the flow structure for different phases of the beat period are observed as well as the processes of switching the flow between the magnetic poles of the accretor. Numerical calculations of the asynchronous system are performed under the assumption of the dipole configuration of the magnetic field for different values of the dipole offset relative to the center of the white dwarf. The paper presents a method for estimating this offset from observational light curves.