Large-scale magnetic geometry of the G8 dwarf xi Bootis A
Pascal Petit (Max-Planck Institut für Aeronomie)
We investigate the magnetic geometry of the active G8 dwarf xi Bootis A, from spectropolarimetric observations obtained in the summer of 2003 with the MuSiCoS échelle spectropolarimeter at the Télescope Bernard Lyot (Observatoire du Pic du Midi, France). We repeatedly detect a photospheric magnetic field, with periodic variations consistent with rotational modulation of period 6.43 days. A direct modelling of the circularly polarized line profiles suggests that the large-scale field is constituted of two mains components, with an inclined dipole and a large-scale toroidal field. This result provides a confirmation, based on independent modelling techniques, to previous detections of large-scale azimuthal fields on cool active stars achieved with the help of Zeeman-Doppler Imaging.
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