Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-11-14
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
abstract modified, figures 4 and 5 slightly corrected; discussion modified; accepted MNRAS
Scientific paper
We investigate the stability of partially ionised, differentially rotating, diffusive disc threaded by both azimuthal and vertical magnetic field. The general stability criterion of such a disc in the presence of axisymmetric fluctuations can be stated purely in terms of ambipolar and Hall diffusivities. It is shown that the disc is magnetorotationally unstable if the sum of scaled ambipolar and Hall diffusivities are larger than some numerical constant determined by the rotation profile of the disc. This criterion suggests that the diffusive discs are always unstable to almost radial fluctuations. The field geometry and obliqueness of wavevector (encapsulated together in the topological factor $g$), plays dual role of not only assisting MRI in ambipolar--Ohm dominated disc but also making otherwise stable region in Hall--ambipolar diffusion plane unstable.
Pandey B. P.
Wardle Mark
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