Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

The strange magnetic fields of white dwarf stars

mercredi 24 août 2016, par John D Landstreet (Western Univ., London, Ontario, Canada)

Jeudi 6 octobre 2016 à 14h00 , Lieu : Salle de confĂ©rence du bâtiment 17

We have observational detections of magnetic fields in at least some stars of the major stages of stellar evolution, from the pre-main sequence to the commonest stellar final state, the white dwarfs. However, the evolution of a field as a star evolves from one stage to another is still very poorly understood. The white dwarfs are particularly puzzling. Naively, their fairly rare megaGauss magnetic fields could be the descendents, by flux conservation, of the fairly rare kiloGauss magnetic fields of upper main sequence stars. But how these main sequence fields survive the giant and AGB stages of stellar evolution, or how “new" fields are produced in some young white dwarfs (perhaps by binary merger events) is still far from clear. Theoretical advances depend on a good foundation of observations to test and refine models. S. Bagnulo, G. Valyavin and I have been working to provide a systematic observational description of the occurrence and field geometry of magnetic white dwarfs, especially close to the weak field limit of the very broad observed field strength distribution. In the course of this work, which uses data from ESO FORS, WHT ISIS, and the Russian 6-m telescope, we have developed a powerful method of using ESPaDOnS on the CFHT to detect and ultimately model very weak white dwarf fields. This talk will survey some of our interesting first results.