2013A&A...549L...5G -
Astronomy and Astrophysics, volume 549, L5-5 (2013/1-1)
What controls the magnetic geometry of M dwarfs?
GASTINE T., MORIN J., DUARTE L., REINERS A., CHRISTENSEN U.R. and WICHT J.
Abstract (from CDS):
Observations of rapidly rotating M dwarfs show a broad variety of large-scale magnetic fields encompassing dipole-dominated and multipolar geometries. In dynamo models, the relative importance of inertia in the force balance, which is quantified by the local Rossby number, is known to have a strong impact on the magnetic field geometry. We aim to assess the relevance of the local Rossby number in controlling the large-scale magnetic field geometry of M dwarfs. We have explored the similarities between anelastic dynamo models in spherical shells and observations of active M-dwarfs, focusing on field geometries derived from spectropolarimetric studies. To do so, we constructed observation-based quantities aimed to reflect the diagnostic parameters employed in numerical models. The transition between dipole-dominated and multipolar large-scale fields in early to mid M dwarfs is tentatively attributed to a Rossby number threshold. We interpret late M dwarfs magnetism to result from a dynamo bistability occurring at low Rossby number. By analogy with numerical models, we expect different amplitudes of differential rotation on the two dynamo branches.
Abstract Copyright:
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Journal keyword(s):
dynamo - magnetohydrodynamics (MHD) - stars: magnetic field - stars: rotation - stars: low-mass - brown dwarfs
Simbad objects:
3
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