Issue |
A&A
Volume 478, Number 1, January IV 2008
|
|
---|---|---|
Page(s) | 1 - 8 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361:20077172 | |
Published online | 20 November 2007 |
Stability of toroidal magnetic fields in rotating stellar radiation zones
1
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482, Potsdam, Germany e-mail: [lkitchatinov;gruediger]@aip.de
2
Institute for Solar-Terrestrial Physics, PO Box 291, Irkutsk 664033, Russia e-mail: kit@iszf.irk.ru
Received:
26
January
2007
Accepted:
14
October
2007
Aims.Two questions are addressed as to how strong magnetic fields can be stored in rotating stellar radiation zones without being subjected to pinch-type instabilities and how much radial mixing is produced if the fields are unstable.
Methods.Linear equations are derived for weak disturbances of magnetic and velocity fields, which are global in horizontal dimensions but short–scaled in radius. The linear formulation includes the 2D theory of stability to strictly horizontal disturbances as a special limit. The eigenvalue problem for the derived equations is solved numerically to evaluate the stability of toroidal field patterns with one or two latitudinal belts under the influence of rigid rotation.
Results.Radial displacements are essential for magnetic instability.
It does not exist in the 2D case of strictly horizontal
disturbances. Only stable (magnetically modified) r-modes are
found in this case. The instability recovers in 3D. The minimum
field strength for onset of the instability and
radial scales of the most rapidly growing modes are strongly
influenced by finite diffusion, the scales are indefinitely short if
diffusion is neglected. The most rapidly growing modes for the Sun
have radial scales of about 1 Mm. In the upper part of the solar
radiation zone,
600 G. The toroidal field can
exceed this value only marginally, for otherwise the radial mixing
produced by the instability would be too strong to be compatible
with the observed lithium abundance.
Key words: instabilities / magnetohydrodynamics (MHD) / stars: interiors / stars: magnetic fields / Sun: magnetic fields
© ESO, 2008
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