O. Cohen, J. J. Drake, V. L. Kashyap
We study the effect of a white dwarf on the spin-down of a cataclysmic
variable system using a three-dimensional magnetohydrodynamic numerical model.
The model includes the stellar corona, the stellar wind, and the WD mass and
magnetic field. The existence of the WD modifies the system spin-down by
physically blocking the stellar wind, restructuring the wind, channeling the
wind towards the WD surface, and by modifying the shape and size of the
Alfv\'en surface. The combination of these processes differs among a set of
simple test cases, and the resulting angular momentum loss rates vary by
factors of 2-3, and by factors of two relative to a test model with a single M
dwarf. While the model employs some simplifications, the results suggest
angular momentum loss schemes currently employed in cataclysmic variable
studies do not require drastic revision. Insights are also gained on wind
accretion. We find that efficient accretion switches on quite rapidly with
decreasing orbital separation. Accretion rates depend on magnetic field
alignment and should be modulated by magnetic cycles on the M dwarf. For
particular values of white dwarf magnetic field strength, an efficient
syphoning of coronal plasma from the inward facing M dwarf hemisphere occurs.
Wind accretion rates are expected to vary by factors of 10 or more between
fairly similar close binaries, depending on magnetic field strengths and
orbital separation.
View original:
http://arxiv.org/abs/1201.0998
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