arXiv subjects

V. M. Chechetkin

Publications and source records attributed to V. M. Chechetkin.

25 records · Page 2Linked to original sources

arXiv1998

Spherical Bondi accretion onto a magnetic dipole

Quasi-spherical supersonic (Bondi-type) accretion to a star with a dipole magnetic field is investigated using resistive magnetohydrodynamic simulations. A systematic study is made of accretion to a non-rotating star, while sample results for a rotating star are also presented. A new stationary subsonic accretion flow is found with a steady rate of accretion to the magnetized star smaller than the Bondi accretion rate. Dependences of the accretion rate and the flow pattern on the magnetic momentum of the star and the magnetic diffusivity are presented. For slow star's rotation the accretion flow is similar to that in non-rotating case, but in the case of fast rotation the structure of the subsonic accretion flow is fundamentally different and includes a region of ``propeller'' outflow. The methods and results described here are of general interest and can be applied to systems where matter accretes with low angular momentum.

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arXiv1998

Hydrodynamic Simulations of Counterrotating Accretion Disks

Hydrodynamic simulations have been used to study accretion disks consisting of counterrotating components with an intervening shear layer(s). Configurations of this type can arise from the accretion of newly supplied counterrotating matter onto an existing corotating disk. The grid-dependent numerical viscosity of our hydro code is used to simulate the influence of a turbulent viscosity of the disk. Firstly, we consider the case where the gas well above the disk midplane rotates with angular rate +Ω(r) and that well below has the same properties but rotates with rate -Ω(r). We find that there is angular momentum annihilation in a narrow equatorial boundary layer in which matter accretes supersonically with a velocity which approaches the free-fall velocity and the average accretion speed of the disk can be enormously larger than that for a conventional α-disk rotating in one direction. Secondly, we consider the case of a corotating accretion disk for r r_t. In this case we observed, that matter from the annihilation layer lost its stability and propagated inward pushing matter of inner regions of the disk to accrete. Thirdly, we investigated the case where counterrotating matter inflowing from large radial distances encounters an existing corotating disk. Friction between the inflowing matter and the existing disk is found to lead to fast boundary layer accretion along the disk surfaces and to enhanced accretion in the main disk. These models are pertinent to the formation of counterrotating disks in galaxies and possibly in Active Galactic Nuclei and in X-ray pulsars in binary systems.

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arXiv1998

The Influence of Parameters on the Flow Structure in Semidetached Binary Systems: 3D Numerical Simulation

The basic parameters determining the flow pattern for a nonviscous, non-heat-conducting gas in a semidetached binary system without a magnetic field are identified. Three-dimensional gas-dynamical modeling of the mass transfer enables investigation of the influence of these parameters on the structure of gas flows. The parameter on which the flow pattern depends most strongly is the adiabatic index $γ$. The effect of other parameters is small, and only leads to unimportant quantitative changes in the solutions obtained. The main properties of flows typical of semidetached binaries without magnetic fields are summarized.

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arXiv1998

3D numerical simulation of gaseous flows structure in semidetached binaries

The results of 3D hydrodynamic simulation of mass transfer in semidetached binaries of different types (cataclysmic variables and low-mass X-ray binaries) are presented. We find that taking into account of 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 gas stream from the inner Lagrangian point L1 and forming accretion disc. The stream deviates under the action of gas of circumbinary envelope, and does not cause the shock perturbation of the disc boundary (traditional `hotspot'). At the same time, the gas of 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 observations. The comparison of synthetic light curves with observations proves the validity of the discussed hydrodynamic model without `hotspot'. We also consider the influence of a circumbinary envelope on the mass transfer rate in semidetached binaries. The obtained features of flow structure in the vicinity of L1 show that the gas of circumbinary envelope plays an important role in the flow dynamics, and that it leads to significant (in order of magnitude) increasing of the mass transfer rate. The comparison of gaseous flows structure obtained in 2D and 3D approaches is presented. We discuss the common features of the flow structures and the possible reasons of revealed differences.

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arXiv1998

Evidence for the Absence of a Stream-Disk Shock Interaction (Hot Spot) in Semi-Detached Binary Systems. Comparison of Numerical Simulation Results and Observations

The results of three-dimensional numerical simulations of the flow of matter in non-magnetic semidetached binary systems are presented. Self-consistent solutions indicate the absence of a shock interaction between the stream of matter flowing from the inner Lagrange point and the accretion disk (a "hot spot"). At the same time, the interaction between the stream and the common envelope of the system forms an extended shock wave along the edge of the stream, whose observational properties are roughly equivalent to those of a hot spot in the disk. Comparison of synethesized and observed light curves confirm the adequacy of the proposed model for the flow of matter without formation of a hot spot. The model makes it possible for the first time to reproduce the variety of the observed light curves of cataclysmic variables in the framework of a single model, without invoking additional assumptions.

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arXiv1998

Impact of a Binary System Common Envelope on Mass Transfer through the Inner Lagrange Point

Results of numerical simulations of the impact of a common envelope on the matter flow pattern near the outflowing component in a semidetached binary system are presented. Three-dimensional modeling of the matter transfer gas dynamics in a low-mass X-ray binary X1822-371 enable investigation of the structure of flows in the vicinity of the inner Lagrange point L1. Taking into account the common envelope of the system substantially changes the flow pattern near the Roche surface of the outflowing component. In a stationary regime, accretion of common envelope gas is observed over a significant fraction of the donor star's surface, which inhibits the flow of gas along the Roche surface to L1. The change in the flow pattern is particularly significant near L1, where the stream of common envelope gas strips matter off the stellar surface. This, in turn, significantly increases (by an order of magnitude) the gas flow from the donor surface in comparison with the estimates of standard models.

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arXiv1998

Three-dimensional Modeling of the Matter Flow Structure in Semidetached Binary Systems

Results of numerical simulations of matter flows in a semidetached binary system similar to the low-mass X-ray binary X1822--371 are presented. Three-dimensional modeling of the mass transfer gas dynamics makes it possible to investigate gas streams in the system and to study the influence of a common envelope. The presence of the common envelope leads to the absence of shock interaction between the stream of matter flowing from the inner Lagrange point and the gas in the accretion disk. The stream is deflected by the gas in the common envelope and approaches the disk tangentially, so that it does not cause any shock perturbation ("hot spot") on the disk. At the same time, the interaction of the stream with the common envelope leads to the formation of an extended shock wave along the edge of the stream. The observational manifestation of this shock is estimated to be equivalent to that of a hot spot in the disk. The calculated accretion disk parameters are presented.

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