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 } \times 10 ^ { -9 } M _ { \odot } yr ^ { -1 } .
The photospheric absorption lines are narrow , and we use the Fourier transform technique to infer v \sin i = 15 \pm 3 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 .