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Astron. Astrophys. 334, 736-741 (1998)


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On the dynamo driven accretion disks

Chun-Yu Ma 1, 2 and Peter L. Biermann 1

1 Max-Planck Institute für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 Purple Mountain Observatory, Academia Sinica, Nanjing 210008, P.R. China

Received 10 October 1997 / Accepted 11 February 1998

Abstract

We add the [FORMULA] effect in the dynamo driven accretion disk model proposed by Tout & Pringle (1992), i.e., a dynamo model depends on the physical processes such as Parker instability, B-H instability, magnetic field reconnection and [FORMULA] mean field dynamo as well. The [FORMULA] effect in the dynamo mechanism is determined by the strength of turbulence of the accretion flow. When the turbulent Mach number [FORMULA] is less than 0.25, the solutions of the magnetic fields oscillate around their equilibrium values. Increasing the value of [FORMULA] makes the amplitude of the oscillation smaller and the period longer, but does not affect the equilibrium values. The Shakura-Sunyaev viscosity parameter [FORMULA] oscillates around the equilibrium value of 0.33. When the turbulent Mach number [FORMULA] is larger than 0.25, the magnetic field components reach a stable state. In the non-linear dynamo region, the critical turbulent Mach number [FORMULA] is 0.44 rather than 0.25. The oscillating magnetic fields and viscosity parameter can explain the basic properties of the dwarf nova eruptions and some properties of quiescent disks (Armitage et al. 1996).

Key words: magnetic fields – MHD – instabilities – accretion, accretion disks – turbulence

Present address: Department of Mathematics and Statistics, Memorial University of Newfoundland, St John's, NF, A1C 5S7, Canada

Send offprint requests to: Chun-Yu Ma, (cyma@math.mun.ca)

© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998

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