Guildford Astronomical Society

Natalie Rees

Natalie Rees - Credit: Natalie ReesNatalie Rees
Credit: Natalie Rees

Natalie is currently a PhD student at the University of Surrey under the supervision of Dr Robert Izzard.
Before this, she completed her undergraduate and masters degrees in astrophysics at the University of Cambridge, during which she realised she had a particular interest for all things stars.
Her current work is focusing on improving computational models of asymptotic giant branch stars, which will then be used to investigate the process of common envelope evolution in binary systems.
DateTalk at GAS meeting
20 May 2021A Zoom Talk: AGB (Asymptotic giant branch) stars : thermal pulses, third dredge-up and binary interactions

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.