Pre-supernova O-C shell mergers could produce more 44Ti than the explosion
Abstract
The formation of 44Ti 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 44Ti and other radioactive isotopes. We compare a range of observations and models of explosive 44Ti yields to pre-explosive multi-zone mixing-burning nucleosynthesis simulations of an O-C shell merger in a 15~M Z=0.02 stellar model with mixing conditions corresponding to different 3D hydro mixing scenarios. Radioactive species produced in the O shell have a multi-dex spread in pre-explosive yield predictions across different 3D mixing scenarios of 1.54~dex and 2.14~dex on average depending on mass cut. 44Ti has the largest spread of 4.78~dex and 4.81~dex depending on mass cut. Further, we show that the pre-explosive production of 44Ti can be larger than the explosive production of models and can match observations. Our results also show that 3D mixing physics enhances 44Ti in 1D models without modifying 56Ni yields. We conclude that quantitative predictions of 44Ti and other radioactive species more broadly require an understanding of the 3D hydrodynamic mixing conditions present during the O-C shell merger.
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