Emily E. Whitehead | Searcharxiv

arXiv2025

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.

astro-ph.SR↗

arXiv2024

Evolving massive stars to core collapse with GENEC: Extension of equation of state, opacities and effective nuclear network

Stars with initial mass above roughly 8 solar masses will evolve to form a core made of iron group elements at which point no further exothermic nuclear reactions between charged nuclei may prevent the core collapse. Electron captures, neutrino losses, and the photo-disintegration of heavy nuclei trigger the collapse of these stars. Models at the brink of core collapse are produced using stellar evolution codes and these pre-collapse models may be used in the study of the subsequent dynamical evolution (including their explosion as supernovae and the formation of compact remnants such as neutron stars or black holes). We upgrade the physical ingredients employed by the GENeva stellar Evolution Code, GENEC, so that it may cover the regime of high temperatures and high densities required to produce progenitors of core-collapse. We have improved GENEC in three directions, equation of state, the nuclear reaction network and the radiative and conductive opacities adapted for the computation of the advanced phases of evolution. We produce a small grid of pre-supernova models of stars with zero-age main sequence masses of 15, 20 and 25 solar masses at solar and less than half solar metallicities. The results are compared with analogous models produced with the MESA code. The global properties of our new models, particularly of their inner cores, are comparable to models computed with MESA and pre-existing progenitors in the literature. Between codes the exact shell structure varies impacting explosion predictions. Using GENEC with state-of-the-art physics, we have produced massive stellar progenitors prior to collapse. These progenitors are suitable for follow-up studies, including the dynamical collapse and supernova phases. Larger grids of supernova progenitors are now feasible, with potential for further dynamical evolution.

astro-ph.SR↗