The asymptotic giant branch (AGB) is a late stage in the evolution of intermediate mass stars. These stars are extremely luminous, with outer layers that are cool and expanded, causing them to be found in the upper right portion of the Hertzsprung-Russell diagram.
By this point in the star’s lifetime, helium has been exhausted in the core leading to a carbon and oxygen rich core surrounded by separate helium and hydrogen burning shells. The double shell burning results in dramatic thermal pulses when helium ignites under degenerate conditions in a thin shell.
The pulses give rise to the phenomena of third dredge-up where material from the core (primarily carbon) is mixed all the way up to the surface, where it can be detected by observers.
AGB stars are also thought to be the location of the slow-neutron capture process (s-process) which produces heavy elements such as barium and lead, making them important contributors to the galactic chemical evolution.
In addition, AGB stars are also likely to interact with a binary companion due to their large size and strong stellar winds, resulting in mass transfer and potentially even common envelope evolution.
This talk will investigate all of these processes and how they lead to a variety of different observed stars including carbon stars, nitrogen-rich stars, S stars, barium stars, cataclysmic variables and red stragglers.