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C. Litwin, R. Rosner, D.Q. Lamb (Univ. of Chicago)
The problem of plasma penetration of astrophysical magnetospheres is an important issue in a wide variety of contexts. We point out that under well--defined conditions, deep penetration can occur without any turbulent mixing (driven, e.g., by Rayleigh--Taylor or Kelvin--Helmholtz instabilities) postulated in the past. Specifically, in binary stellar systems with the Roche lobe overflow, the accretion stream can penetrate even if its ram pressure is smaller than the magnetic pressure. The particular mechanism responsible for cross--field propagation is an E-cross-B drift caused by an electric field arising from polarization currents in the accretion stream. Depolarization effects result in a drag on the plasma flow and limit the penetration depth. Estimating the drag force resulting from magnetic field-aligned currents, we determine the criteria for deep magnetosphere penetration; in particular, we find that deep penetration results for sufficiently narrow streams (such as suggested by the analysis of Lubov & Shu 1975), and for sufficiently low ambient plasma densities and temperatures.
Research supported by the U.S. Department of Energy.
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