Formation of accretion disks in close-binary systems with magnetic fields

Жилкин, А. Г.; Bisikalo, D. V.

doi:10.1134/s1063772910120012

Cited by 21 publications

(34 citation statements)

References 37 publications

(65 reference statements)

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“…This code was used in [27,29,30] to investigate the flow structure in a close binary system (SS Cyg was taken as an example) with a relatively weak, purely dipolar magnetic field (10 5 G at the surface). A modification of the code was introduced in [31], which enables simulations of systems with strong dipolar magnetic fields (10 7 −10 8 G).…”

Section: Introductionmentioning

confidence: 99%

Full 3D MHD calculations of accretion flow structure in magnetic cataclysmic variables with strong, complex magnetic fields

2012

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We have performed three-dimensional magnetohydrodynamical calculations of stream accretion in cataclysmic variable stars for which the white dwarf primary possesses a strong, complex magnetic field. These calculations were motivated by observations of polars: cataclysmic variables containing white dwarfs with magnetic fields sufficiently strong to prevent the formation of an accretion disk. In this case, an accretion stream flows from the L 1 point and impacts directly onto one or more spots on the surface of the white dwarf. Observations indicate that the white dwarfs in some binaries possess complex (non-dipolar) magnetic fields. We performed simulations of ten polars, with the only variable being the azimuthal angle of the secondary with respect to the white dwarf. These calculations are also applicable to asynchronous polars, where the spin period of the white dwarf differs by a few percent from the orbital period. Our results are equivalent to calculating the structure of one asynchronous polar at ten different spin-orbit beat phases. Our models have an aligned dipolar plus quadrupolar magnetic field centered on the whitedwarf primary. We find that, with a sufficiently strong quadrupolar component, an accretion spot arises near the magnetic equator for slightly less than half our simulations, while a polar accretion zone is active for most of the remaining simulations. For two configurations, accretion at a dominant polar region and in an equatorial zone occurs simultaneously. Most polar studies assume that the magnetic field is dipolar, especially for single-pole accretors. We demonstrate that, with the orbital parameters and magnetic-field strengths typical of polars, the accretion flow patterns can vary widely in the case of a complex magnetic field. This may make it difficult for many polars to determine observationally whether the field is pure dipolar or is more complex, but there shoulid be indications for some systems. In particular, a complex magnetic field should be suspected if there is an accretion zone near the white dwarf's equator (assumed to be in the orbital plane) or if there are two or more accretion regions that cannot be fitted by dipolar magnetic field. Magnetic-field constraints are expected to be substantially stronger for asynchronous polars, with clearer signs of complex field geometry due to changes in the accretion flow structure as a function of azimuthal angle. These indications become clearer in asynchronous polars because each azimuthal angle corresponds to a different spin-orbit beat phase.

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Section: Introductionmentioning

confidence: 99%

Full 3D MHD calculations of accretion flow structure in magnetic cataclysmic variables with strong, complex magnetic fields

2012

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“…We run our binary wind simulation using the magnetohydrodynamics code Nurgush (Zhilkin & Bisikalo 2010). Nurgush solves the hydrodynamic equations in three dimensions using a non-inertial coordinate system that rotates with the orbital motion of the two stars.…”

Section: Methodsmentioning

confidence: 99%

Colliding winds in low-mass binary star systems: wind interactions and implications for habitable planets

Johnstone

Жилкин

Pilat-Lohinger

et al. 2015

A&A

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Context. In binary star systems, the winds from the two components impact each other, leading to strong shocks and regions of enhanced density and temperature. Potentially habitable circumbinary planets must continually be exposed to these interaction regions. Aims. We study, for the first time, the interactions between winds from low-mass stars in a binary system to show the wind conditions seen by potentially habitable circumbinary planets. Methods. We use the advanced 3D numerical hydrodynamic code Nurgush to model the wind interactions of two identical winds from two solar mass stars with circular orbits and a binary separation of 0.5 AU. As input into this model, we use a 1D hydrodynamic simulation of the solar wind, run using the Versatile Advection Code. We derive the locations of stable and habitable orbits in this system to explore what wind conditions potentially habitable planets will be exposed to during their orbits. Results. Our wind interaction simulations result in the formation of two strong shock waves separated by a region of enhanced density and temperature. The wind-wind interaction region has a spiral shape due to Coriolis forces generated by the orbital motions of the two stars. The stable and habitable zone in this system extends from ∼1.4 AU to ∼2.4 AU. Habitable planets have to pass through strong shock waves several times per orbit and spend a significant amount of time embedded in the higher density matter between the shocks. The enhanced density in the wind-wind interaction region is likely to lead to a 20% decrease in the size of a planet's magnetosphere. Conclusions. Our results indicate that wind-wind interactions are likely to influence the magnetospheres and upper atmospheres of circumbinary planets and could have moderate implications for the development of habitable planetary environments.

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“…To investigate how the value of the magnetic field influences the flow structure, we have performed calculations with various values of B a in a range from 10 5 to 10 8 G (Zhilkin & Bisikalo 2010c). Let us consider seven models, with values of the magnetic induction equal to: 10 5 G (model 1), 5 × 10 5 G (model 2), 10 6 G (model 3), 5 × 10 6 G (model 4), 10 7 G (model 5), 5 × 10 7 G (model 6), and 10 8 G (model 7).…”

Section: Changes In the Flow Structure With Increasing Of The Magnetimentioning

confidence: 99%

“…However, since the problem is very complicated, the investigations have been performed either in the frame of simplified models (King 1993;Wynn & King 1995;Wynn et al 1997;King & Wynn 1999;Norton et al 2004;Ikhsanov et al 2004;Norton et al 2008), or in a limited region of the stellar magnetosphere (Koldoba et al 2002;Romanova et al 2003Romanova et al , 2004aRomanova et al , 2004b. Only over the last few years, the authors have managed to develop a comprehensive 3D numerical model to calculate the flow structure in close binaries (Zhilkin & Bisikalo 2009, 2010a, 2010b, 2010c. In our approach, we use a complete system of MHD equations that allows one to describe all 510 D. V. Bisikalo & A. G. Zhilkin the main dynamic effects concerned with the magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Flow Structure in Magnetic CVs

Бисикало

Жилкин

2011

Proc. IAU

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Abstract. We present a review of the modern concept of physical processes which go on in magnetic CVs with the mass transfer between the components. Using results of 3D MHD simulations, we investigated variations of the main characteristics of accretion disks depending on the value of the magnetic induction on the surface of the accreting star. In the frame of a self-consistent description of the MHD flow structure in close binaries, we formulate conditions of the disk formation and find a criterion that separates two types of flows corresponding to intermediate polars (intermediate magnetic field) and polars (strong field).The influence of asynchronous rotation of the accretor on the flow structure in magnetic close binaries is also discussed. Simulations show that the accretion instability arising in binaries with rapid rotation of accretor ("propeller" regime) can explain the mechanism of quasi-periodic dwarf nova outbursts observed in DQ Her systems.

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Formation of accretion disks in close-binary systems with magnetic fields

Cited by 21 publications

References 37 publications

Full 3D MHD calculations of accretion flow structure in magnetic cataclysmic variables with strong, complex magnetic fields

Full 3D MHD calculations of accretion flow structure in magnetic cataclysmic variables with strong, complex magnetic fields

Colliding winds in low-mass binary star systems: wind interactions and implications for habitable planets

Flow Structure in Magnetic CVs

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