The Impact of Initial Mass Dependent Convective Boundary Mixing on the Structure and Fates of Massive Stars

While convection has been known to play a key role in stars for many decades, its implementation in one-dimensional stellar evolution codes still represents a major uncertainty today. The purpose of this work is to investigate the impact of initial mass dependent convective boundary mixing (CBM), often referred to as overshooting, on the frequency and type of nuclear burning shell interactions that occur in low metallicity massive stars and the subsequent effect on their fates. Two grids of models were calculated using the Modules for Experiments in Stellar Astrophysics (MESA) code and a 22-isotope nuclear network, each with a different strength of CBM applied. One grid uses the typical CBM value for diffusive overshooting used in literature whereas the other grid uses CBM values guided by the results of 3D convection simulations. Interactions between the carbon, neon and oxygen shells (C-Ne-O) are common throughout both grids. The higher CBM grid also exhibits more frequent H-He and He-C interactions at lower initial masses than in the lower CBM grid. Several models also undergo multiple interaction events during evolution. While future work will be needed to fully assess the impact of the new CBM and the interactions it leads to, one expects interesting effects like unusual nucleosynthesis including more common or enhanced i- and gamma-process nucleosynthesis. Furthermore, SN precursors and a significant change to the pre-SN structure are also expected, with many models not having the commonly expected onion-ring like structure and having a different explosion probability.