Amanda Karakas

Bespoke models of AGB and post-AGB stars

New observations of asymptotic giant branch (AGB) and post-AGB stars are challenging our understanding of the evolution of low and intermediate-mass stars. Gaia-derived luminosities of S-type AGB stars are particularly interesting in this regard. S-type stars are thought to be showing the first signs of third dredge-up mixing, and are good candidates for calibrating models. However the luminosity of an AGB star does not provide a unique initial (or current) stellar mass, owing to the core-mass luminosity relationship which is degenerate for stars less than 2 solar masses. In this talk I summarise our efforts to derive the initial masses of S-type AGB stars from their stellar pulsations. Surveys of post-AGB stars in the LMC and SMC have also discovered objects with surface compositions showing large enrichments in carbon and elements heavier than iron. Some of these post-AGB stars have luminosities that are lower than predicted by carbon-rich AGB models, making them challenging to explain. In this talk I present the results of new stellar evolutionary models designed to reproduce observations of low-luminosity AGB and post-AGB stars, including their heavy-element surface compositions.