Binary stars and magnetic fields

Abstract
We examine the effect of binary companions and magnetic fields on stellar evolution. Today our understanding of the former is good though far from complete. We single out common envelope evolution as the least satisfactory and illustrate the effects of our lack of knowledge on the population synthesis of type Ia supernovae. We currently fare much worse with magnetic fields and so concentrate on what we do know and where this breaks down. Combining both aspects we examine what role magnetic fields might play in common envelope evolution.