Monthly Notices Of The Royal Astronomical Society
We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the Telescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of -810 +/- 150 and +680 +/- 190 G, implying a minimum surface dipole polar strength of 2850 +/- 500 G. In contrast, we derive an upper limit (3 sigma) to the primary's surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission - previously interpreted as a consequence of colliding stellar winds - in this context. We conclude that HD 47129 represents a heretofore unique stellar system - a close, massive binary with a rapidly rotating, magnetized component - that will be a rich target for further study.
J. H. Grunhut, G. A. Wade, M. A. Leutenegger, V. Petit, G. Rauw, C. Neiner, F. Martins, David H. Cohen, M. Gagné, R. Ignace, S. Mathis, S. E. De Mink, A. F.J. Moffat, S. P. Owocki, M. Shultz, and J. O. Sundqvist.
"Discovery Of A Magnetic Field In The Rapidly Rotating O-Type Secondary Of The Colliding-Wind Binary HD 47129 (Plaskett's Star)".
Monthly Notices Of The Royal Astronomical Society.