Journal Article

Helicity and dynamo action in magnetized stellar radiation zones

G. Rüdiger, L. L. Kitchatinov and D. Elstner

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 425, issue 3, pages 2267-2276
Published in print September 2012 | ISSN: 0035-8711
Published online September 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21569.x
Helicity and dynamo action in magnetized stellar radiation zones

Show Summary Details

Preview

Abstract

The helicity and α effect driven by the non-axisymmetric Tayler instability of toroidal magnetic fields in stellar radiation zones are computed. In the linear approximation, a purely toroidal field always excites pairs of modes with identical growth rates but with opposite helicity so that the net helicity vanishes. If the magnetic background field has a helical structure by an extra (weak) poloidal component then one of the modes dominates, producing a net kinetic helicity anticorrelated with the current helicity of the background field. The mean electromotive force is computed with the result that the α effect by the most rapidly growing mode has the same sign as the current helicity of the background field. The α effect is found to be too small to drive an α2 dynamo, but the excitation conditions for an αΩ dynamo can be fulfilled for weak poloidal fields. Moreover, if the dynamo produces its own α effect by the magnetic instability, then problems with its sign do not arise. For all cases, however, the α effect shows an extremely strong concentration to the poles so that a possible αΩ dynamo might only work at the polar regions. Hence, the results of our linear theory lead to a new topological problem for the existence of large-scale dynamos in stellar radiation zones on the basis of the current-driven instability of toroidal fields.

Keywords: instabilities; MHD; stars: interiors; stars: magnetic field

Journal Article.  6402 words.  Illustrated.

Subjects: Astronomy and Astrophysics

Full text: subscription required

How to subscribe Recommend to my Librarian

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.