On the magnetic field and circumstellar environment of the young O7 star 1 Orionis C *
J.-F. Donati 1 and
G.A. Wade 2
Received 23 July 1998 / Accepted 6 October 1998
We present new circular spectropolarimetric observations of the young O-type star Orionis C obtained with the MuSiCoS échelle spectropolarimeter and the 2 m Télescope Bernard Lyot, in an attempt to detect the surface magnetic field structure invoked to explain the periodic variability of Ori C at X-ray, UV and optical wavelengths. We obtain null detections with 250 G 1 error bars for the disc-averaged line-of-sight (i.e. longitudinal) component of the surface magnetic field vector, from which we conclude that the polar strength of the dipole field structure is lower than 1.6 to 2.0 kG (with a confidence level of 87%), depending on the exact orientation of the magnetic and rotation axes with respect to the line of sight.
We report as well the unexpected discovery of strong, time variable continuum circular polarisation in the spectrum of Ori C, as well as depolarisation structures associated with nebular emission lines, indicating that this continuum polarisation (the nature of which is as yet unclear) is produced within the immediate circumstellar environment.
Key words: polarization stars: circumstellar matter stars: early-type stars: individual: 1 Ori C stars: magnetic fields
Send offprint requests to: J.-F. Donati
© European Southern Observatory (ESO) 1999
Online publication: November 26, 1998