P. Petit, M. Aurière, R. Konstantinova-Antova, A. Morgenthaler, G. Perrin, T. Roudier, J. -F. Donati
We present the outcome of a highly-sensitive search for magnetic fields on
the cool supergiant Betelgeuse. A time-series of six circularly-polarized
spectra was obtained using the NARVAL spectropolarimeter at T\'elescope Bernard
Lyot (Pic du Midi Observatory), between 2010 March and April. Zeeman signatures
were repeatedly detected in cross-correlation profiles, corresponding to a
longitudinal component of about 1 G. The time-series unveils a smooth increase
of the longitudinal field from 0.5 to 1.5 G, correlated with radial velocity
fluctuations. We observe a strong asymmetry of Stokes V signatures, also
varying in correlation with the radial velocity. The Stokes V line profiles are
red-shifted by about 9 km/s with respect to the Stokes I profiles, suggesting
that the observed magnetic elements may be concentrated in the sinking
components of the convective flows.
View original:
http://arxiv.org/abs/1109.3979
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