A numerical model for accretion in intermediate polars with dipolar magnetic fields

Abstract

A three-dimensional numerical model for an accretion process investigation in the magnetosphere of a white dwarf in magnetic cataclysmic variables is developed. The model assumes that the white dwarf has a dipole magnetic field with its symmetry axis inclined to the rotation axis. The model is based on the equations of modified MHD, that describe the mean flow parameters in the wave MHD turbulence. Diffusion of the magnetic field and radiative heating and cooling are taken into account. The suitability of the model is confirmed by modeling the accretion in a typical intermediate polar. The computations show that a magnetosphere forms around the accretor, with the accretion occurring via columns. The accretion columns have a curtain-like shape, and arc-shaped zones of energy release form on the surface of the white dwarf in the magnetic poles area as a result of the matter infall.

Laboratory study of stationary accretion shock relevant to astrophysical systems

“…The cooling parameter is defined as the ratio of the cooling time to the characteristic hydrodynamical timescale χ = t cool / t hyd and is a measure of the importance of radiative effects. Values for the astrophysical system are taken from 13,27 .…”

“…Of particular interest are the subclasses of systems known as polars or intermediate polars, the former being characterised by a single optical and X-ray photometric period and strong optical linear (5–10%) and circular (10–80%) polarisation. Due to the very strong magnetic field of the white dwarf ( B ~ 0.01–1 MG for intermediate polars and up to B > 10 MG for polars), the accreting plasma flow ( υ ~ 1000 km/s) is guided along the field lines onto the WD photosphere, forming a column rather than an accretion disk 11–13 . After impact on the WD photosphere, a radiative reverse shock is formed, which propagates counter to the incoming flow, thus heating the accretion column to temperatures up to 10 keV.…”

Hot Spots Drift in Synchronous and Asynchronous Polars: Results of Three-Dimensional Numerical Simulation

“…This model is based on the equations system of modified magnetic hydrodynamics, which describes astrophysical flows under conditions of a strong external magnetic field. We have successfully applied this approach to modeling the flow structure for both polars and intermediate polars [5,[16][17][18][19][20][21][22][23][24][25][26][27][28].…”

Features of the accretion in the EX Hydrae system: Results of numerical simulation

“…To estimate the opening angles of the curtain, we performed 3D numerical simulations of the magnetosphere structure in the EX Hya system, applying the model described in [3]. In the computations, we adopted the magnetic field at the accretor surface B a = 8 kG and the inclination of the magnetic axis to the rotation axis of the white dwarf 30 • .…”

“…The interaction of the magnetic field and the plasma of the accretion disk results in the formation of a magnetosphere near the white dwarf. Accretion onto the white dwarf proceeds via accretion columns, that have a curtain-like shape and are mainly oriented along magnetic field lines [3]. The basic parameters of EX Hya are listed in the table 1 (see, e. g., [4]).…”