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Science 3 February 2006:
Vol. 311. no. 5761, pp. 633 - 635
DOI: 10.1126/science.1121102
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Reports

The Large-Scale Axisymmetric Magnetic Topology of a Very-Low-Mass Fully Convective Star

Jean-François Donati,1* Thierry Forveille,2 Andrew Collier Cameron,3 John R. Barnes,3 Xavier Delfosse,4 Moira M. Jardine,3 Jeff A. Valenti5

Understanding how cool stars produce magnetic fields within their interiors is crucial for predicting the impact of such fields, such as the activity cycle of the Sun. In this respect, studying fully convective stars enables us to investigate the role of convective zones in magnetic field generation. We produced a magnetic map of a rapidly rotating, very-low-mass, fully convective dwarf through tomographic imaging from time series of spectropolarimetric data. Our results, which demonstrate that fully convective stars are able to trigger axisymmetric large-scale poloidal fields without differential rotation, challenge existing theoretical models of field generation in cool stars.

1 Laboratoire d'Astrophysique de Toulouse-Tarbes, Observatoire Midi-Pyrénées, 14 avenue Exxxx Belin, F-31400 Toulouse, France.
2 Canada-France-Hawaii Telescope, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, USA.
3 School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, Scotland KY16 9SS, UK.
4 Laboratoire d'Astrophysique de l'Observatoire de Grenoble, Université Joseph Fourier, 31 rue de la Piscine, F-38041 Grenoble, France.
5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA.

* To whom correspondence should be addressed. E-mail: jean-francois.donati{at}ast.obs-mip.fr

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Science. ISSN 0036-8075 (print), 1095-9203 (online)