Cool Stars 14 - Submitted Abstract # 115
This version created on 05 October 2006

First detection of molecular circular polarization in starspots


S.V. Berdyugina, Institute of Astronomy ETH Zurich
P. Petit, Observatoire Midi-Pyrenees, Toulouse
D.M. Fluri, Institute of Astronomy ETH Zurich 
N. Afram, Institute of Astronomy ETH Zurich
J. Arnaud, Observatoire Midi-Pyrenees, Toulouse

We report on the first ever detection of circular polarization in
molecular lines forming in magnetic regions on the surfaces of active
stars.  The new observations were obtained with the high-resolution
spectro-polarimeter ESpADOnS recently installed at the
Canada-France-Hawaii Telescope.  We carried out a survey of G-K-M
stars including young main-sequence dwarfs and RS CVn-type giants and
subgiants.  All stars were found to possess surface magnetic fields
producing Stokes V LSD signals in atomic lines of 0.05% to 0.5%.
Several stars clearly showed circular polarization in molecular lines
of 0.5% to 1%.  The molecular Stokes V signal is reminiscent to that
observed in sunspots.  Modeling the observed polarization allows us
for the first time to diagnose the magnetic field in the coolest parts
of spatially unresolved starspots and reveal their internal structure.

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