X-ray emission and the incidence of magnetic fields in the massive stars of the Orion Nebula Cluster

Abstract

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.