Magnetospheres & Winds

The circumstellar magnetic field of tau Sco

Massive stars aren't expected to harbor magnetic fields, due to their lack of a sub-surface convection zone to act as a field-generating dynamo. In spite of this, strong (~kG) fields are observed in a number of objects, including the helium-strong chemically peculiar stars (e.g., σ Ori E), the helium-weak stars (e.g., 36 Lyn) and a few more-massive O-type stars (e.g., θ1 Ori C; τ Sco, shown above). With new generations of high-resolution spectropolarimeters such as ESPaDOnS, the list of magnetic massive stars continues to grow; recent additions include V* NU Ori and V* LP Ori (see Petit et al. 2008).

Within the Massive Stars Group, our primary focus is on the observation and theory of magnetospheres — the circumstellar environments where the dynamics of wind outflows are significantly affected by the presence of the magnetic field. In the standard magnetically confined wind shock (MCWS) paradigm developed by Babel & Montmerle (1997), a sufficiently strong field can channel the supersonic wind into a head-on collision with itself. The resulting shocks heat the wind material to high temperatures (~107 K), explaining why observations of many magnetic massive stars (e.g., Gagné et al. 2005) reveal them to be moderately hard (≥ 1 keV) X-ray sources.


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