Large-scale magnetic topologies of early M dwarfs ⋆

• Main Authors: J. -f. Donati, J. Morin, P. Petit, X. Delfosse, T. Forveille, M. Aurière, R. Cabanac, B. Dintrans, R. Fares, T. Gastine, M. M. Jardine, F. Lignières, F. Paletou, J. C. Ramirez Velez, S. Théado
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2008
• Subjects: narval
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.311.5303; http://arxiv.org/pdf/0809.0269v1.pdf

We present here additional results of a spectropolarimetric survey of a small sample of stars ranging from spectral type M0 to M8 aimed at investigating observationally how dynamo processes operate in stars on both sides of the full convection threshold (spectral type M4). The present paper focuses on early M stars (M0–M3), i.e. above the full convection threshold. Applying tomographic imaging techniques to time series of rotationally modulated circularly polarised profiles collected with the NARVAL spectropolarimeter, we determine the rotation period and reconstruct the large-scale magnetic topologies of 6 early M dwarfs. We find that early-M stars preferentially host large-scale fields with dominantly toroidal and non-axisymmetric poloidal configurations, along with significant differential rotation (and long-term variability); only the lowest-mass star of our subsample is found to host an almost fully poloidal, mainly axisymmetric large-scale field ressembling those found in mid-M dwarfs. This abrupt change in the large-scale magnetic topologies of M dwarfs (occuring at