Speaker: Jonathan Braithwaite, Argelander Institut für Astronomie, Universität Bonn, Bonn, Germany

Title: Weak magnetic fields in early-type stars

Abstract: Recently weak (~ gauss) magnetic fields have been detected in the main-sequence A stars Vega and Sirius, and it seems likely that all A stars contain fields of at least this strength. I review two theories for the origins of these fields: (a) a "failed fossil" theory where the field is continuously evolving from some field inherited from birth and (b) a dynamo mechanism residing in a subsurface convection layer. Both theories seem equally plausible at present, so I describe some observations which could distinguish between them. In contrast, in more massive stars (O and early B) magnetic fields from subsurface convection seems very likely but with current technology probably not directly measurable, so I briefly discuss some indirect observational signatures of such magnetic fields.