A model of astrophysical tori with magnetic fields

A steady axisymmetric model of magnetohydrodynamical tori is constructed under the assumptions that the specific angular momentum is constant in whole space and the magnetic field has only the toroidal component. Furthermore, the gas is assumed to be polytropic and the magnetic field is supposed to be expressed by a power of the density and the radius in some specified manner. The relativistic effect is simulated by use of a pseudo-Newtonian potential. It is found that the configuration of the torus with a toroidal magnetic field is elongated along the symmetry axis because of the dominance by the magnetic field far from the axis. Furthermore, the position of the bottom where the density is maximum approaches the center in comparison with the case without magnetic field, although the shape of the funnel and the location of the cusp do not change. In order for such MHD tori to exist, the values of the parameters, e.g., the specific angular momentum and the Alfven speed at the bottom are restricted in some ranges. (author)