The strange magnetic fields of white dwarf stars
University of Western Ontario
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 hardly 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. I have been working with Stefano Bagnulo and Gena Valyavin to provide a systematic observational description of the occurrence and field geometry of magnetic white dwarfs close to the weak field limit of the very broad observed field strength distribution. In the course of this work, 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 on the kiloGauss stars WD2047+372 and WD2359-434, and on non-magnetic 40 Eri B.
Date: Thursday, 26 January 2017 Time: 11:30 Where: Université de Montréal Pavillon Roger-Gaudry, Local D-460 Contact: Gilles Fontaine