Journal Article

Revisiting the Rigidly Rotating Magnetosphere model for σ Ori E – I. Observations and data analysis*

M. E. Oksala, G. A. Wade, R. H. D. Townsend, S. P. Owocki, O. Kochukhov, C. Neiner, E. Alecian and J. Grunhut

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 419, issue 2, pages 959-970
Published in print January 2012 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19753.x
Revisiting the Rigidly Rotating Magnetosphere model for σ Ori E – I. Observations and data analysis*

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We have obtained 18 new high-resolution spectropolarimetric observations of the B2Vp star σ Ori E with both the Narval and ESPaDOnS spectropolarimeters. The aim of these observations is to test, with modern data, the assumptions of the Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki, applied to the specific case of σ Ori E by Townsend, Owocki & Groote. This model includes a substantially offset dipole magnetic field configuration, and approximately reproduces previous observational variations in longitudinal field strength, photometric brightness and Hα emission. We analyse new spectroscopy, including H i, He i, C ii, Si iii and Fe iii lines, confirming the diversity of variability in photospheric lines, as well as the double S-wave variation of circumstellar hydrogen. Using the multiline analysis method of least-squares deconvolution (LSD), new, more precise longitudinal magnetic field measurements reveal a substantial variance between the shapes of the observed and RRM model time-varying field. The phase-resolved Stokes V profiles of He i 5876 and 6678 Å lines are fitted poorly by synthetic profiles computed from the magnetic topology assumed by Townsend et al.. These results challenge the offset dipole field configuration assumed in the application of the RRM model to σ Ori E, and indicate that future models of its magnetic field should also include complex, higher order components.

Keywords: techniques: spectroscopic; circumstellar matter; stars: early-type; stars: individual: HD 37479; stars: magnetic field; stars: rotation

Journal Article.  6331 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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