Impact of the magnetic field on the structure of accretion disks in semi-detached binaries

We discuss characteristic features of the magnetic gas-dynamical structure of the flows in a semi-detached binary system obtained from three-dimensional simulations, assuming that the intrinsic magnetic field of the accreting star is dipolar. The turbulent diffusion of the magnetic field is taken into account. The SS Cyg system is considered as an example. Including the magnetic field can alter the basic parameters of the accretion disk, such as the accretion rate and the characteristic density. The magnetic field in the disk is primarily toroidal.     

The influence of the inclination of the accretor’s magnetic axis on the accretion-disk structure in intermediate polars

Typical changes of the accretion-disk structures in intermediate polars are studied as a function of the inclination of the accretor’s magnetic field. Thre-dimensional numerical modeling was performed for seven differentmagnetic-axis inclinations. The results showthat the system forms a magnetosphere region, and that column accretion occurs. The action of the magnetic field tilts the inner parts of the disk along the magnetic axis of the accretor. The magnetic-field inclination appreciably influences matter transfer in the disk and accretion processes. Generation of toroidal magnetic field, magnetic braking, and alignment of the dipole magnetic field result in oscillations of the accretion rate. A direct relationship between the field inclination and the oscillation amplitude is found, as well as an inverse relationship between the field inclination and the oscillation period.     

Self-similar regimes for the collapse of magnetic protostellar clouds

Self-similar solutions describing the homogeneous, free, isothermal collapse of protostellar clouds are considered. One such solution correponds to the critical case of the propagation of a rarefaction wave near the time when it is focused in the central region of the cloud. The speed of the rarefaction front is finite and equal to three times the isothermal sound speed. The asymptotic distributions of gas-dynamical quantities in the central part of the collapsing cloud and the surrounding envelopes are considered at both early and late stages of compression, after the formation of an opaque core (protostar). These solutions are used in a magneto-kinematic approximation to study the geometry and evolution of the large-scale magnetic fields of collapsing protostellar clouds. All the solutions are verified using direct numerical simulations. It is shown that an initially uniform magnetic field acquires an “hourglass” geometry with time. The characteristic opening angles in the self-similar solutions are in satisfactory agreement with observations.     

The matter-flow structure in the SS Cyg system in its quiescent state from comparisons of observational and synthetic Doppler tomograms

Doppler tomograms are constructed for the quiescent state of the SS Cyg system based on Hβ and Hγ spectral-line observations carried out in August 2006 with the 2-m telescope at Terskol Peak. Gasdynamical simulations combined with the Doppler tomograms enable identification of the main features of the flow. Comparisons of synthetic tomograms with observations indicate that an accretion disk is present in the quiescent system. In the tomograms, the luminosity is maximum at the arms of the spiral tidal shock at the shock front due to the interaction between the gas of the circum-binary envelope and material in the stream issuing from the Lagrangian point L₁ (the “hot line”), and in the region behind the bow shock due to the motion of the accretor and disk in the gas of the envelope. The contribution of this last element results in appreciable asymmetry of the tomograms.     

Features of the matter flows in the peculiar cataclysmic variable AE Aquarii

The structure ofmatter flows in close binary systems in which one of the components is a rapidly rotating magnetic white dwarf is studied. Themain example considered is the AEAquarii system; the period of the white dwarf’s rotation is about a factor of 1000 shorter than the orbital period, and the magnetic field on the white-dwarf surface is of order 50MG. The matter flows in this system were analyzed via numerical solution of a systemofmagnetohydrodynamical equatons. These computations show that the white dwarf’s magnetic field does not significantly influence the velocity field of the matter in its Roche lobe in the case of a laminar flow regime, so that the field does not hinder the formation of a transient disk (ring) surrounding the magnetosphere. However, the efficiency of the energy and angular-momentum exchange between the white dwarf and the surrounding matter increases considerably with the development of turbulent motions in the matter, accelerating the matter at the magnetosphere boundary and leading to a high escape rate from the system. The time scales for the system’s transition between the laminar and turbulent modes are close to those for the transition of AE Aquarii between its quiet and active phases.     

Three-Dimensional Model of the Flow Structure in the Asynchronous Polar CD Ind during Magnetic Pole Switching

Astronomy Reports - We performed a three-dimensional numerical MHD simulation of the flow structure in the asynchronous polar CD Ind during the switching phases between the magnetic poles of the...     

A Possible Mechanism for the Radio Emission of Polars

Astronomy Reports - A means of generating the radio emission of polars is proposed, based on cyclotron radiation of thermal electrons in a fluctuating magnetic field. The source of these...     

Effect of Variations in the Extended Hydrogen Corona of Mars on the Efficiency of Charge Exchange with Solar Wind Protons

Astronomy Reports - This paper presents the results of calculating the efficiency of solar wind proton charge exchange as a function of variations in the column density of hydrogen atoms in the...     

Magnetic-field structure in the accretion disks of semi-detached binary systems

The results of three-dimensional MHD numerical simulations are used to investigate the characteristic properties of the magnetic-field structures in the accretion disks of semi-detached binary systems. It is assumed that the intrinsic magnetic field of the accretor star is dipolar. Turbulent diffusion of the magnetic field in the disk is taken into account. The SS Cyg system is considered as an example. The results of the numerical simulations show the intense generation of a predominantly toroidal magnetic field in the accretion disk. Magnetic zones with well defined structures for the toroidal magnetic field form in the disk, which are separated by current sheets in which there ismagnetic reconnection and current dissipation. Possible observational manifestations of such structures are discussed. It is shown that the interaction of a spiral precessional wave with the accretor’s magnetosphere could lead to quasi-periodic oscillations of the accretion rate.     

Possible Electromagnetic Manifestations of Merging Black Holes

Astronomy Reports - The scenario of a merger of two black holes surrounded by an accretion disk is considered. As a result of the emission of gravitational waves, the mass of the central object...