Veronique Petit (ULAVAL) 

Title: On the X-ray emission and the incidence of magnetic field in
massive stars of the Orion Nebula Cluster

Abstract: Magnetic fields have been frequently proposed as a likely
source of variability and confinement of the winds of massive
stars. Recently, Stelzer et al. (2005) found significant X-ray
emission from all massive stars in the Orion Nebula Cluster
(ONC). Periodic rotational modulation in X-rays and other indicators
suggested that there might be many magnetic B- and O-type stars in
this star-forming region.  We have carried out sensitive ESPaDOnS
observations to search for direct evidence of such fields, detecting
unambiguous Zeeman signatures in three objects. We also obtained
dipole field upper limits for the remaining stars with a
state-of-the-art Bayesian analysis, resulting in a precise magnetic
characterisation of all ONC massive stars. This allows us to explore
for the first time the connections between fields, winds and X-rays in
a complete, co-eval and co-environmental sample of massive
stars. These remarkable results bring forth new challenges for
understanding the processes leading to X-ray emission in massive
stars.  We also expect to provide unique data regarding the incidence
of magnetic fields in massive stars with which to confront models of
magnetic field origin in neutron stars and magnetars, such as that
proposed by Ferrario & Wickramasinghe (2006).