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Paper: Accretion-disk structure with magnetic fields
Volume: 261, The Physics of Cataclysmic Variables and Related Objects
Page: 317
Authors: RĂ¼diger, G.
Abstract: The role of a large-scale magnetic field in a star-disk system is discussed. The central object may yield a magnetic dipolar field which is modified by the disk, and also the disk structure is strongly influenced. For rather weak magnetic fields there is no disk inside the corotation radius, but outside the corotation radius the disk becomes warmer, thicker and more massive than the corresponding nonmagnetic solution. Another situation holds if the halo is not corotating, so that the vertical shear generates toroidal magnetic fields at the upper and lower disk surfaces. The resulting vertical angular momentum flow strongly influences the inwards directed accretion flow and the disk structure as well. The main consequence of a such model, however, concerns the dragging problem of the magnetic field lines in the halo. A critical angle of 30circ between the field line and the disk normal must be exceeded in order to launch cold jets. Such values are now easily resulting even for the low magnetic Prandtl numbers which are realistic for turbulent accretion disks Pm <~1). The magnetic disk is thicker than a nonmagnetic one for typical parameter values. The accretion rate can be strongly amplified for large inclination angle and small magnetic Prandtl number. The surface values of the toroidal magnetic fields which are necessary to be induced in order to generate high values for the inclination angle are much smaller than expected. Finally, new results are presented of recent 2D simulations of an accretion disk under the presence of a vertical magnetic field. Density, temperature, accretion flow, rotation and magnetic field are computed in the R-Z-plane. Of particular interest, of course, is the interface between the disk and its magnetosphere. My colleagues M. Küker (Jena), Chr. Fendt (Potsdam), D. Elstner (Potsdam) and D. Shalybkov (St. Petersburg) are acknowledged for close collaborations and discussions about the presented subject.
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