X-ray emission and the incidence of magnetic fields in the massive stars   of the Orion Nebula Cluster
  Magnetic fields have been frequently invoked as a likely source of variability and confinement of the winds of massive stars. To date, the only magnetic field detected in O-type stars are those of theta 1 Ori C (HD 37022; Donati et al. 2002), the brightest and most massive member of the Orion Nebula Cluster (ONC), and HD 191612 (Donati et al. 2006). Notably, theta 1 Ori C is an intense X-ray emitter, and the source of these X-rays is thought to be strong shocks occurring in its magnetically-confined wind (Babel & Montmerle 1997a, Donati et al. 2002).   Recently, Stelzer et al. (2005) found significant X-ray emission from all massive stars in the ONC. Periodic rotational modulation in X-rays and other indicators suggested that theta 1 Ori C may be but one of many magnetic B- and O-type stars in this star-forming region. In 2005B we carried out sensitive ESPaDOnS observations to search for direct evidence of such fields, detecting unambiguous Zeeman signatures in two objects. 
V. Petit, G.A. Wade, T. Montmerle, Drissen, N. Grosso, F. Menard