Paper:	Polarimetric Observations of σ Orionis E
Volume:	464, Circumstellar Dynamics at High Resolution
Page:	413
Authors:	Carciofi, A. C.; Faes, D. M.; Townsend, R. H. D.
Abstract:	Some massive stars possess strong magnetic fields that confine plasma in the circumstellar environment. These magnetospheres have been studied spectroscopically, photometrically and, more recently, interferometrically. Here we report on the first firm detection of a magnetosphere in continuum linear polarization, as a result of a monitoring of σ Ori E done at the Pico dos Dias Observatory. A rotational modulation of the polarization was observed, with a period of half of the rotation period, which supports the theoretical prediction on the presence of two diametrally opposed, co-rotating blobs of gas. A phase lag of –0.08 was detected between the polarization minimum and the primary minimum of the light curve, suggestive of a complex shape of the plasma clouds. We present a preliminary analysis of the data with the Rigidly Rotating Magnetosphere model, which could not reproduce correctly the shape and the level of the polarization curve. A simple toy model consisting on two spherical co-rotating blobs proved more successful in explaining the polarization modulation. This result suggests that imaging polarimetry can provide a diagnostic of the geometry of clouds, which will serve as useful constraints for the Rigidly Rotating Magnetosphere model.

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