Structure and magnetic configurations of accretion disk-dynamo models

The influence of large-scale magnetic fields on the structure of accretion disks is studied. The magnetic field is obtained by a self-consistent nonli near dynamo model with magnetic pressure strongly influencing the density s tratification which itself feeds back to the field generation. The resultin g magnetic field geometry is discussed in relation to the accretion disk wi nd theory. Regarding new results of MHD turbulence simulations, both possible signs of the oc-effect are allowed (Brandenburg & Donner 1997). In the canonical ca se of positive alpha the resulting field is of quadrupolar symmetry. The fi eld strength is about 50% of the value for dynamo models nonlinearly limite d by alpha-quenching. The temperature profiles as well as the disk geometry remain nearly unchanged. The viscous stress remains the key transporter of angular momentum driving the accretion inflow. For negative alpha, however, a stationary dipolar structure of the magnetic field results. The additional magnetic torque at the disk surface changes the profile of the effective temperature significantly to a profile which i s more flat. The magnetic torque becomes of the same order as the radial vi scous torque. The inclination angle of the poloidal field exceeds 30 degree s even for a magnetic Prandtl number of order unity, and also the criterion for poloidal collimation after Spruit et al. (1997) is fulfilled. The dyna mo-generated magnetic field configuration thus supports the magnetic wind l aunching concept for accretion disks for realistic turbulent magnetic Prand tl numbers.