ADVANCED BURNING STAGES AND FATE OF 8-10<i>M</i>_☉STARS

Abstract

The stellar mass range 8&lt;M/Mo&lt;12 corresponds to the most massive AGB stars\nand the most numerous massive stars. It is host to a variety of supernova\nprogenitors and is therefore very important for galactic chemical evolution and\nstellar population studies. In this paper, we study the transition from\nsuper-AGB star to massive star and find that a propagating neon-oxygen burning\nshell is common to both the most massive electron capture supernova (EC-SN)\nprogenitors and the lowest mass iron-core collapse supernova (FeCCSN)\nprogenitors. Of the models that ignite neon burning off-center, the 9.5Mo model\nwould evolve to an FeCCSN after the neon-burning shell propagates to the\ncenter, as in previous studies. The neon-burning shell in the 8.8Mo model,\nhowever, fails to reach the center as the URCA process and an extended (0.6 Mo)\nregion of low Ye (0.48) in the outer part of the core begin to dominate the\nlate evolution; the model evolves to an EC-SN. This is the first study to\nfollow the most massive EC-SN progenitors to collapse, representing an\nevolutionary path to EC-SN in addition to that from SAGB stars undergoing\nthermal pulses. We also present models of an 8.75Mo super-AGB star through its\nentire thermal pulse phase until electron captures on 20Ne begin at its center\nand of a 12Mo star up to the iron core collapse. We discuss key uncertainties\nand how the different pathways to collapse affect the pre-supernova structure.\nFinally, we compare our results to the observed neutron star mass distribution.\n