8th HEAD Meeting, 8-11 September, 2004
Session 15 Black Holes Binaries and Intermediate Mass Black Holes
Poster, Thursday, September 9, 2004, 9:00am-10:00pm

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[15.02] Accretion to a Rotating Star with Misaligned Dipole Magnetic Field: Results of 2D and 3D Simulations

M.M. Romanova, M. Long, R.V.E. Lovelace (Astronomy Dept., Cornell University), G.V. Ustyugova (Keldysh Inst. of Appl. Math, Moscow, Russia), A.V. Koldoba (Institute of Math. Modelling, Moscow, Russia)

We analyze interaction of a magnetized star with an accretion disk in 2D and 3D MHD simulations. Special quasi-equilibrium initial conditions were applied so that we observed for the first time slow viscous accretion from the disk to the star through the funnel streams, both, in 2D and 3D simulations. 3D simulations were performed at different misalignment angles \Theta, where \Theta is an angle between the magnetic and the rotational axis. Many aspects of the disk-star interaction were investigated for the first time such as: (1) the structure of the inner regions of the disk, (2) the structure of the funnel streams, (3) matter flux and angular momentum fluxe into or out from the star. We observed that in both 2D and 3D dimensions the star either spins-up, or spins-down, or is in the quasi-equilibrium state depending on the ratio between the co-rotation and magnetospheric radii. The regime of very fast rotation of the star (``propeller" regime, where the co-rotation radius is much smaller than the magnetospheric radius) was also investigated. We observed that in this regime the star strongly spins-down. However, matter continues to accrete to the star through modified funnel streams. The accretion often has quasi-periodic nature. Quasi-periodic accretion is often observed at different parameters of the model. The quasi-periodicity is connected with accumulation and release of the magnetic flux through reconnection events. This research was supported by NASA and NSF.

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