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Recent papers on astro-ph Wind
Accretion to Dipole Disk
Accretion to Dipole The Origin of Jets Accretion
Disks Theory Extrasolar Planets
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DISK ACCRETION TO MAGNETIZED STARS 3D MHD SIMULATIONS OF DISK ACCRETION TO AN INCLINED ROTATOR. MAGNETOSPHERIC FLOW AT DIFFERENT Q [abstract] [full text] [plots from the paper] [animation]
(2) At a small inclination angle Q = 5°, the densest matter accretes in two streams which precess around the star's rotation axis with angular velocity larger than that of the star. The high velocity of precession is connected with the fact that inner regions of the disk rotate faster than the star, while the streams rotate with intermediate velocity. The lower density matter covers the whole magnetosphere, but forms lower-density windows, which also precess around the rotational axis. Precessing streams and windows may lead to quasi-periodic variability of the star.
(4) At the even larger inclination angle, Q = 45°, matter flows in two or several streams. These streams may also modulate the star's emission. Variability of the accretion rate will lead to variation of the flow pattern in the magnetosphere. Recently Muzerolle, Calvet, & Hartmann (2001), suggested that some observations of CTTSs may be explained if the funnel flows have a multiple stream geometry.
(6) The inner regions of the disk are often warped or tilted. This tilt is connected with the fact that matter leaving the disk and entering the magnetosphere has a strong tendency to co-rotate with the magnetosphere, so that the inner tilted disk has an axis close to that of the dipole m axis. We never observed the warp in the direction predicted by theory because the twist of the magnetic field lines, which is necessary for such warp, is always small.
(8) Magnetic braking leads to significant departure of the angular velocity of the disk from Keplerian in the region r < 2 for smaller inclination angles, and for r < 3 for larger inclination angles. At Q = 60° and Q = 75° a significant part of the disk up to r ~ 2.4 almost co-rotates with the star. (9) The accretion rate in the established flow dM /dt is approximately the same for a wide variety of inclination angles, Q = 5° - 45° with slightly larger values for Q = 60° and Q = 75° . We conclude that dependence of the accretion rate on Q is not very high. These values approximately coincide with the accretion rate obtained in analogous two-dimensional simulations. The accretion rate associated with pure hydrodynamic accretion is about 10 times smaller. (10) We observed that angular momentum is transported from the disk to the star and that it is carried mainly by the magnetic field near the stellar surface. The same situation was observed in our two-dimensional axisymmetric simulations. For the considered small angular velocity of the star, the angular momentum flux relative to the Z axis gives a positive torque Nz which acts to spin-up of the star for all Q. In addition, we have derived from our simulations the torques Nx and Ny which are found to be non-zero for non-zero inclination angles Q. These torques act to shift the direction of the angular momentum of the star. Most
of simulation runs were done for T = 5 - 12 rotations of the inner radius
of the disk. This time is sufficient for understanding the physics of the
process, because the initial
relaxation occurs in T ~ 0.5 - 2 rotations depending on Q.
Two-dimensional axisymmetric simulations, which were done up to T ~ 50 -
80 rotations, have shown that the magnetospheric flow settles at T ~ 1 and
later all features of the flow are very similar during many many
rotations. This provides support for physical applicability of
our simulation results. Nevertheless, one of the planned developments is
to generate longer runs with a steady inflow of matter from the disk.
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