EDP Sciences
Free Access
Issue
A&A
Volume 450, Number 3, May II 2006
Page(s) 1077 - 1095
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361:20041980
Published online 19 April 2006
A&A 450, 1077-1095 (2006)
DOI: 10.1051/0004-6361:20041980

Stable magnetic fields in stellar interiors

J. Braithwaite1 and Å. Nordlund2

1  Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, Postfach 1317, 85741 Garching, Germany
    e-mail: jon@mpa-garching.mpg.de
2  Department of Astrophysics, Niels Bohr Institute, Juliane Maries Vej 30, 2100 København Ø, Denmark
    e-mail: aake@astro.ku.dk

(Received 9 September 2004 / Accepted 19 December 2005 )

Abstract
We investigate the 50-year old hypothesis that the magnetic fields of the Ap stars are stable equilibria that have survived in these stars since their formation. With numerical simulations we find that stable magnetic field configurations indeed appear to exist under the conditions in the radiative interior of a star. Confirming a hypothesis by Prendergast (1956, ApJ, 123, 498), the configurations have roughly equal poloidal and toroidal field strengths. We find that tori of such twisted fields can form as remnants of the decay of an unstable random initial field. In agreement with observations, the appearance at the surface is an approximate dipole with smaller contributions from higher multipoles, and the surface field strength can increase with the age of the star. The results of this paper were summarised by Braithwaite & Spruit (2004, Nature, 431, 891).


Key words: instabilities -- magnetohydrodynamics (MHD) -- stars: magnetic fields

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