Stellar Duets: how companions shape the lives and evolution of stars
Orsola De Marco
Dept. of Astrophysics, American Museum of Natural History

Stars evolve differently when they have a close companion. When a star expands during its giant phase(s) it can interact with the companion in one of many ways. One such interaction, called common envelope, sees the two stars immersed in the envelope of the primary. The companion and the core of the primary then spiral in towards each other, and the lost orbital energy goes into the ejection of the envelope. The result is a short period evolved binary. The common envelope is responsible for double degenerates, possible progenitors of supernovae type Ia, cataclysmic variables and many other binary classes. Yet, despite common envelopes playing such a role in stellar evolution, our knowledge of this process is still rudimentary. In this talk I will introduce the physics of the common envelope and present numerical simulations to try and understand its workings. Planetary nebulae are thought to be the ejecta of intermediate mass stars, bound to become white dwarfs in the near future. Yet, their fantastic shapes, as well as many aspects of their evolution, are difficult to explain with current single star theory. A hypothesis that planetary nebulae are primarily a binary interaction phenomenon has recently been reconsidered. I will present out efforts to test this hypothesis observationally, and how planetary nebulae can be used to test our theoretical understanding of binary interactions.

Date:	Jeudi, le 16 octobre 2008
Heure:	12:15
Lieu:	Université de Montréal
	Pavillon Roger-Gaudry, Local D-460
Contact:	Pierre Bergeron