Pre-supernova O-C shell mergers could produce more ${}^{44}\mathrm{Ti}$ than the explosion

Abstract

The formation of ${}^{44}\mathrm{Ti}$ in massive stars is thought to occur during explosive nucleosynthesis, however recent studies have shown it can be produced during O-C shell mergers prior to core collapse. We investigate how mixing according to 3D macro physics derived from hydrodynamic simulations impacts pre-supernova O-C shell merger nucleosynthesis and if it can dominate explosive supernova production of ${}^{44}\mathrm{Ti}$ and other radioactive isotopes. We compare a range of observations and models of explosive ${}^{44}\mathrm{Ti}$ yields to pre-explosive multi-zone mixing-burning nucleosynthesis simulations of an O-C shell merger in a $15{\mathrm{M}}_{\odot }$ $Z=0.02$ stellar model with mixing conditions corresponding to different 3D hydro mixing scenarios. Radioactive species produced in the $\mathrm{O}$ shell have a multi-dex spread in pre-explosive yield predictions across different 3D mixing scenarios of $1.54\mathrm{dex}$ and $2.14\mathrm{dex}$ on average depending on mass cut. ${}^{44}\mathrm{Ti}$ has the largest spread of $4.78\mathrm{dex}$ and $4.81\mathrm{dex}$ depending on mass cut. Further, we show that the pre-explosive production of ${}^{44}\mathrm{Ti}$ can be larger than the explosive production of models and can match observations. Our results also show that 3D mixing physics enhances ${}^{44}\mathrm{Ti}$ in 1D models without modifying ${}^{56}\mathrm{Ni}$ yields. We conclude that quantitative predictions of ${}^{44}\mathrm{Ti}$ and other radioactive species more broadly require an understanding of the 3D hydrodynamic mixing conditions present during the O-C shell merger.

Accepted by ApJ, 10 pages, 5 figures, 2 tables