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arXiv · 1003.3626

Discovery of a strong magnetic field in the rapidly rotating B2Vn star HR 7355

M. E. Oksala·G. A. Wade·W. L. F. Marcolino·J. Grunhut·D. Bohlender·N. Manset·R. H. D. Townsend·the MiMeS Collaboration
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Abstract

We report the detection of a strong, organized magnetic field in the helium-variable early B-type star HR 7355 using spectropolarimetric data obtained with ESPaDOnS on the 3.6-m Canada-France-Hawaii Telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Program. HR 7355 is both the most rapidly rotating known main-sequence magnetic star and the most rapidly rotating helium-strong star, with $v \sin i$ = 300 $\pm$ 15 km s$^{-1}$ and a rotational period of 0.5214404 $\pm$ 0.0000006 days. We have modeled our eight longitudinal magnetic field measurements assuming an oblique dipole magnetic field. Constraining the inclination of the rotation axis to be between $38^{\circ}$ and $86^{\circ}$, we find the magnetic obliquity angle to be between $30^{\circ}$ and $85^{\circ}$, and the polar strength of the magnetic field at the stellar surface to be between 13-17 kG. The photometric light curve constructed from HIPPARCOS archival data and new CTIO measurements shows two minima separated by 0.5 in rotational phase and occurring 0.25 cycles before/after the magnetic extrema. This photometric behavior coupled with previously-reported variable emission of the H$α$ line (which we confirm) strongly supports the proposal that HR 7355 harbors a structured magnetosphere similar to that in the prototypical helium-strong star, $σ$ Ori E.

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M. E. Oksala, G. A. Wade, W. L. F. Marcolino, J. Grunhut, D. Bohlender, N. Manset, R. H. D. Townsend, the MiMeS Collaboration. 2010-03-18. Discovery of a strong magnetic field in the rapidly rotating B2Vn star HR 7355. https://doi.org/10.1111/j.1745-3933.2010.00857.x

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