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Astron. Astrophys. 342, 892-900 (1999)


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An [FORMULA]-dynamo in accretion disks with linear force-free coronae

M. Reyes-Ruiz 1 and T.F. Stepinski 2

1 Instituto de Astronomía, UNAM, Apdo. Postal 877, 22800 Ensenada, B.C. México
2 Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA

Received 25 March 1998 / Accepted 22 September 1998

Abstract

We investigate the generation of a large-scale magnetic field by an [FORMULA]-dynamo in turbulent accretion disks surrounded by linear force-free coronae. The standard [FORMULA]-disk model with parameters relevant to a typical disk around a compact star is assumed. The dynamo-generated magnetic field is calculated in both kinematic and nonlinear regimes. The critical dynamo number is [FORMULA] and the lowest normal mode has a quadrupole symmetry, just like dynamo models calculated for disks surrounded by a vacuum. The equilibrated magnetic field also has quadrupole symmetry and its distribution inside the disk is almost the same as in a disk with vacuum exterior. The novel feature is the existence of a toroidal field in the exterior of the disk which, permits the corona to transmit magnetic stresses between the inner and outer parts of the disk. However, all dynamical effects of the large-scale magnetic fields are small, due to the restricted magnitude and the specific configuration of the magnetic field generated by the [FORMULA]-dynamo.

Key words: Accretion, accretion disks – MHD

Send offprint requests to: M. Reyes-Ruiz

© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999

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