Journal Article

Magnetic field evolution of white dwarfs in strongly interacting binary star systems

Adrian T. Potter and Christopher A. Tout

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 2, pages 1072-1080
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2009.15935.x
Magnetic field evolution of white dwarfs in strongly interacting binary star systems

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The surface magnetic field strength of white dwarfs is observed to vary from very little to around 109 G. Here, we examine the proposal that the strongest fields are generated by dynamo action during the common envelope phase of strongly interacting stars that leads to binary systems containing at least one white dwarf. The resulting magnetic field depends strongly on the electrical conductivity of the white dwarf, the lifetime of the convective envelope and the variability of the magnetic dynamo. We assess the various energy sources available and estimate necessary lifetimes of the common envelope. In the case of a dynamo that leads a randomly oriented magnetic field, we find that the induced field is confined to a thin boundary layer at the surface of the white dwarf. This then decays away rapidly upon dispersal of the common envelope. The residual field is typically less than 10−8 times the strength of the external field. Only in the case where there is some preferential direction to the dynamo-generated field can an induced field, which avoids rapid decay, be produced. We show that a surface field of a magnitude a few per cent of the external field may be produced after a few Myr. In this case, the residual field strength is roughly proportional to the lifetime of the dynamo activity.

Keywords: binaries: close; stars: evolution; stars: magnetic fields; white dwarfs

Journal Article.  7383 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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