Magnetic fields in accretion discs
Marthijn de Kool, Geoffrey V. Bicknell, Zdenka Kuncic, PASA, 16 (3), 225.
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Contents Page: Volume 16, Number 3

Magnetic fields in accretion discs

Marthijn de Kool¹
Geoffrey V. Bicknell¹
Zdenka Kuncic²

1. Astrophysical Theory Centre, Research School of Astronomy and Astrophysics, Private Bag, Weston Creek, ACT 2611, Australia
2. Department of Physics and Astronomy, University of Victoria, Box 3055, Victoria, B.C.,V8W 3P6, Canada

Abstract:

This paper summarizes two presentations on the role of magnetic fields in accretion discs given at the Workshop on Magnetic Fields and Accretion, ANU, Canberra, Nov. 12-13 1998. The work

In the first part, which is a summary of part of the paper by Kuncic & Bicknell (1999) we present a formal development of the equations governing the structure of an accretion disc containing magnetohydrodynamic turbulence. The importance of the different terms in the energy and momentum equations is discussed, and a parametrization of the unresolved processes is suggested that could be used to make further progress. It is briefly explored whether an MHD accretion disc can transport a significant part of the gravitational power into a corona by buoyancy.

In the second part (based upon de Kool (1999)) we present some exploratory calculations of the vertical structure of accretion discs, in which non-local dissipation of energy due to the buoyant transport of magnetic field energy is taken into account. It is argued that the efficiency of buoyant magnetic transport depends very strongly on the size of the coherent magnetic regions. If the size of the buoyant cells is not very close to the disc thickness, magnetic energy generated by dynamo action inside the disc will be dissipated locally, and will not be available to transport a significant part of the accretion luminosity into a corona.

Keywords: accretion, accretion discs -- magnetic fields.