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DISK ACCRETION TO MAGNETIZED STARS

THE PROPELLER REGIME OF DISK ACCRETION TO A RAPIDLY ROTATING MAGNETIZED STAR

PROPELLER-DRIVEN OUTFLOWS AND DISK OSCILLATIONS 

[abstract 1] [full text 1] [plots from the paper 1] [animation]
[abstract 2] [full text 2] [plots from the paper 2]

In the propeller regime of disk accretion to a rapidly rotating star, we find from axisymmetric MHD simulations that the disk oscillates strongly and gives quasi-periodic outflows of matter to wide-angle (χ ≈ 45◦ − 60◦) conical winds.

At the same time there is strong field-dominated (or Poynting) outflow of energy, angular momentum and matter along the open field lines extending from the poles of the star. Matter outflows with high velocities and is magnetically driven. The outflows occur for conditions where the magnetic diffusivity and viscosity are significant, av,d > 0.1. For smaller values of the diffusivity, the disk oscillates but no outflows are observed. The observed oscillations and outbursts are a robust result, based on a numerous simulations at different parameters with more than a 100 oscillation periods observed in many runs. The period of oscillations varies in different runs in the range tqpo ~ (5 − 100)P*. It increases with * and Ω*. We observed that the oscillations for relatively large av become highly periodic with definite quasiperiods. More detailed analysis of these features will be reported later. A star spins-down rapidly due to both the disk-magnetosphere interaction and the angular momentumou tflow along the open field lines. The results are applicable to young CTTSs, neutron stars, and cataclysmic variables.

 

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2000-2011, last updated on 19.03.11