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arXiv · 0910.0214

Discovery of a magnetic field in the O9 sub-giant star HD 57682 by the MiMeS Collaboration

J. H. Grunhut·G. A. Wade·W. L. F. Marcolino·V. Petit·H. F. Henrichs·D. H. Cohen·E. Alecian·D. Bohlender·J. -C. Bouret·O. Kochukhov·C. Neiner·N. St-Louis·R. H. D. Townsend·the MiMeS Collaboration
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Abstract

We report the detection of a strong, organised magnetic field in the O9IV star HD 57682, using spectropolarimetric observations obtained with ESPaDOnS at the 3.6-m Canada-France-Hawaii Telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Program. From the fitting of our spectra using NLTE model atmospheres we determined that HD 57682 is a $17^{+19}_{-9}$ M$_{\odot}$ star with a radius of $7.0^{+2.4}_{-1.8}$ R$_\odot$, and a relatively low mass-loss rate of $1.4^{+3.1}_{-0.95}\times10^{-9}$ M$_{\odot}$ yr$^{-1}$. The photospheric absorption lines are narrow, and we use the Fourier transform technique to infer $v\sin i=15\pm3$ km s$^{-1}$. This $v\sin i$ implies a maximum rotational period of 31.5 d, a value qualitatively consistent with the observed variability of the optical absorption and emission lines, as well as the Stokes $V$ profiles and longitudinal field. Using a Bayesian analysis of the velocity-resolved Stokes $V$ profiles to infer the magnetic field characteristics, we tentatively derive a dipole field strength of $1680^{+134}_{-356}$ G. The derived field strength and wind characteristics imply a wind that is strongly confined by the magnetic field.

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J. H. Grunhut, G. A. Wade, W. L. F. Marcolino, V. Petit, H. F. Henrichs, D. H. Cohen, E. Alecian, D. Bohlender, J. -C. Bouret, O. Kochukhov, C. Neiner, N. St-Louis, R. H. D. Townsend, the MiMeS Collaboration. 2009-10-01. Discovery of a magnetic field in the O9 sub-giant star HD 57682 by the MiMeS Collaboration. https://doi.org/10.1111/j.1745-3933.2009.00771.x

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