Equilibrium configuration of the magnetosphere of a star loaded with accreted magnetized mass |
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| Authors: | Yutaka Uchida B C Low |
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| Institution: | (1) Tokyo Astronomical Observatory, University of Tokyo, Mitaka, 181 Tokyo, Japan;(2) High Altitude Observatory, Boulder, 80307 Colorado, USA |
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| Abstract: | Equilibrium configuration of the magnetosphere of a star loaded by the gravitationally accreted plasma having its own magnetic
field is investigated. Axisymmetry around the star’s magnetic axis is assumed for simplicity. It is seen that two distinct
configurations appear for the cases of parallel and antiparallel magnetic field of the accreted plasma with respect to the
star’s magnetic moment. If the external field is antiparallel to the star’s magnetic moment, the stellar magnetosphere is
confined within a spherical region surrounded by the external field with a separatric surface between them. This is an extension
of the case of the spherical accretion of non-magnetic plasma dealt with thus far in connection with the mass accretion by
the degenerate stars in X-ray binaries. It is noticed that the mass slides down along the field lines to the point closest
to the star and is stratified hydrostatically in equilibrium to form a disk in the equatorial plane. The mass loading compresses
the sphere as a whole in this case. If, on the other hand, the external field is parallel to the star’s magnetic moment, there
appears a ring of magnetic neutral point in the equatorial plane. Polar field is open and extends to infinity while the low-latitude
field is closed and faces the external field of opposite polarity across the neutral point. The increase of the loaded mass
in this case causes a shrink of the closed field region, and the open polar flux is increased. Therefore, the transition between
equilibria with small and large amount of the loaded mass requires the reconnection of magnetic lines of force, and the reconnection
of the flux through the magnetic neutral ring is proposed as the mechanism of the steady or the intermittent mass leakage
like the ones postulated for some X-ray bursters.
Visiting Scientist supported by the Japan Society for the Promotion of Sciences. |
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| Keywords: | stellar magnetospheres accretion of magnetized mass X-ray binaries |
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