A search for Magnetic Fields in Massive Stars
Jean-Claude Bouret, Jean-Francois Donati, Ian Howarth, Pascal Petit, Moira Jardine, Claude Catala, John Landstreet, Evelyne Alecian, John Barnes, Thierry Forveille, Frederic Paletou, Nadine Manset

Abstract: Many luminous O and early B stars are known to exhibit signs of intense activity (e.g. anomalously strong X-ray emission, variable optical spectra, presence of circumstellar material) that are very often attributed to the presence of a putative large-scale magnetic field. Since such fields can potentially have a strong impact on the physics and evolution of such stars, it is important to characterise their typical field strengths and topologies accurately. With the advent of the new generation spectropolarimeters, such as ESPaDOnS and NARVAL, detection of the expectedly weak magnetic fields in massive stars becomes within range. Here, we present ESPaDOnS observations allowed to detect a magnetic field in the 06-8 spectrum variable HD 191612 (the second known magnetic O star to date) and to map that of the young B0 star Tau Sco. These results prompt several questions concerning the conditions controlling the presence of magnetic fields in hot stars, and the implications of such fields on the winds and the evolution of massive stars.