Colloquium

Nucleosynthesis in Asymptotic Giant Branch Stars

Dr. Amanda Karakas
McMaster University
Hamilton, Ontario, Canada

Wednesday, August 30, 2006   4:00 p.m.  NSH 118

(Refreshments at 3:30 p.m. NSH 284)

 

The Asymptotic Giant Branch is the last nuclear-burning phase for stars with initial masses between about 0.8 to 8 solar masses, and is very short, comprising less than 1 per cent of the main-sequence lifetime. Nevertheless, it is on the AGB that the richest nucleosynthesis occurs for low and intermediate mass stars. The nucleosynthesis is driven by thermal instabilities of the helium-burning shell, the products of which are mixed to the stellar surface by recurrent mixing episodes. Envelope burning occurs in the most massive AGB stars and also alters the surface composition.  In this talk, I will review the structure, evolution and nucleosynthesis of AGB stars. I will focus on the production of the neutron-rich Mg isotopes in intermediate-mass AGB stars, and a recent effort to address the problem of Ge production in low-mass AGB stars, motivated by observations of planetary nebulae which show enhancements by factors of 3 to 30 times the solar value.