Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 386, Issue 2, Pages 673-687Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2008.13094.x
Keywords
accretion; accretion discs; instabilities; MHD; stars : magnetic fields; stars : oscillations
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Funding
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [0807129] Funding Source: National Science Foundation
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We present results of 3D simulations of magnetohydrodynamics (MHD) instabilities at the accretion disc-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It manifests itself in the form of tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial plane. The shape and number of the tongues changes with time on the inner disc dynamical time-scale. In contrast with funnel flows, which deposit matter mainly in the polar region, the tongues deposit matter much closer to the stellar equator. The instability appears for relatively small misalignment angles, Theta less than or similar to 30 degrees, between the star's rotation and magnetic axes, and is associated with higher accretion rates. The hotspots and light curves during accretion through instability are generally much more chaotic than during stable accretion. The unstable state of accretion has possible implications for quasi-periodic oscillations and intermittent pulsations from accreting systems, as well as planet migration.
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