Journal Article

Large-scale magnetic topologies of mid M dwarfs*

J. Morin, J.-F. Donati, P. Petit, X. Delfosse, T. Forveille, L. Albert, M. Aurière, R. Cabanac, B. Dintrans, R. Fares, T. Gastine, M. M. Jardine, F. Lignières, F. Paletou, J. C. Ramirez Velez and S. Théado

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 2, pages 567-581
Published in print October 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI:
Large-scale magnetic topologies of mid M dwarfs*

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We present in this paper, the first results of a spectropolarimetric analysis of a small sample (∼20) of active stars ranging from spectral type M0 to M8, which are either fully convective or possess a very small radiative core. This study aims at providing new constraints on dynamo processes in fully convective stars.

This paper focuses on five stars of spectral type ∼M4, i.e. with masses close to the full convection threshold (≃0.35 M), and with short rotational periods. Tomographic imaging techniques allow us to reconstruct the surface magnetic topologies from the rotationally modulated time-series of circularly polarized profiles. We find that all stars host mainly axisymmetric large-scale poloidal fields. Three stars were observed at two different epochs separated by ∼1 yr; we find the magnetic topologies to be globally stable on this time-scale.

We also provide an accurate estimation of the rotational period of all stars, thus allowing us to start studying how rotation impacts the large-scale magnetic field.

Keywords: techniques: polarimetric; stars: activity; stars: low-mass, brown dwarfs; stars: magnetic fields; stars: rotation

Journal Article.  9688 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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