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Issue A&A
Volume 423, Number 3, September I 2004
Page(s) 1101 - 1107
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20040435



A&A 423, 1101-1107 (2004)
DOI: 10.1051/0004-6361:20040435

Magnetic activity in late-type giant stars: Numerical MHD simulations of non-linear dynamo action in Betelgeuse

S. B. F. Dorch

The Niels Bohr Institute for Astronomy, Physics and Geophysics, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
    e-mail: dorch@astro.ku.dk

(Received 13 March 2004 / Accepted 10 May 2004 )

Abstract
Evidence is presented from numerical magneto-hydrodynamical simulations for the existence of magnetic activity in late-type giant stars. A red supergiant with stellar parameters similar to that of Betelgeuse ( $\alpha$ Orionis) is modeled as a "star-in-a-box" with the high-order "Pencil Code". Both linear kinematic and non-linear saturated dynamo action are possible: the non-linear magnetic field saturates at a super-equipartition value corresponding to surface magnetic field of field strengths up to ~500 Gauss. In the linear regime two different modes of dynamo action are found with exponential growth rates of ~4 and 25 years, respectively. It is speculated that magnetic activity of late-type giants may influence dust and wind formation and possibly lead to the heating of the outer atmospheres of these stars.


Key words: stars: AGB and post-AGB -- stars: late-type -- stars: activity -- stars: individual: Betelgeuse -- stars: magnetic fields -- magnetohydrodynamic: (MHD)

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