2009MNRAS.400L..94G

We report the detection of a strong, organized 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 Programme. From the fitting of our spectra using non-local thermodynamic equilibrium model atmospheres, we determined that HD 57682 is a 17⁺¹⁹_–9M_☉ star with a radius of 7.0^+2.4_–1.8R_☉ and a relatively low mass-loss rate of 1.4^+3.1_–0.95x 10^–9M_☉/yr. The photospheric absorption lines are narrow, and we use the Fourier transform technique to infer v sini = 15±3 km/s. This v sini implies a maximum rotational period of 31.5d, 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_–356G. The derived field strength and wind characteristics imply a wind that is strongly confined by the magnetic field.