Shear rate dependence and the effect of resistivity in magneto-rotationally unstable, stratified disks

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Corresponding author: U. Ziegler, uziegler@aip.de

Received: 2 November 2000
Accepted: 3 September 2001

Abstract

We study the effect of resistivity and variation of shear rate, , on the magneto-rotational instability in stratified disks. Special attention is paid to dynamo α-action and transport properties of the flow. The 3D magnetohydrodynamical simulations are performed in the local shearing-box approximation employing the code NIRVANA. Due to the chosen type of vertical boundary condition a mean azimuthal magnetic field is generated which is related to dynamo α-action. The corresponding α-parameter is negative (positive) in the northern (southern) disk hemisphere. This result is independent of q ranging between 0.6 and 1.5 and independent of the amount of diffusivity. The magnitude of α typically declines with decreasing q. We suggest a natural limit in the vicinity of below which α-action may be suppressed completely. Resistivity has a significant influence on the magnetic energy level of the final state. It is reduced for decreasing magnetic Reynolds number, Re_m, as one might expect. However, the magneto-rotational instability is able to sustain an angular momentum transport of sufficient amount against diffusion even for the most diffusive case we considered, with . The Shakura-Sunyaev parameter in this case is roughly of that of the non-resistive model with the dominant contribution provided by the Reynolds stress rather than Maxwell stress. The dynamo α-effect is found to vanish for strong dissipation.