Speaker
Description
Super-Asymptotic Giant Branch (super-AGB) stars are intermediate-mass giants of approximately 8-10 Msun, and correspond to the most massive objects that will not undergo a core-collapse supernova explosion. They burn carbon under degenerate conditions and develop oxygen-neon (ONe) cores. Due to an inverted temperature profile in their innermost regions and the prevailing degeneracy, carbon burning proceeds via off-centre flashes, giving rise to associated convective zones and eventually leading to the inward propagation of the carbon-burning flame.
Most super-AGB stars evolve into the thermally-pulsing super-AGB (TP-SAGB) phase and ultimately end their lives as ONe white dwarfs. However, the cores of the most massive ones undergo electron captures on neon and magnesium. Deprived of the electron degeneracy pressure that sustains them, such cores are expected to collapse, triggering an electron-capture supernova (ECSN) explosion.
Despite their predictable theoretical framework, super-AGB stars still harbor intriguing mysteries. For instance, no ECSN has been definitively confirmed observationally to date. The exact efficiency of stellar wind mass loss during the TP-SAGB remains highly uncertain, which alters theoretical predictions of ECSN rates. Furthermore, the nucleosynthesis associated with the "dredge-out” (a proton-ingestion episode occurring at the end of core carbon burning in the most massive super-AGBs) remains poorly understood. Finally, recent re-evaluations of carbon-burning rates may narrow the predicted initial mass ranges that lead to ONe core formation, shifting our understanding of the boundary between white dwarf progenitors and supernovae.