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

Joshua Issa, Falk Herwig

TL;DR

The study asks whether pre-supernova production of $^{44}$Ti during an O-C shell merger can rival or exceed explosive synthesis in massive stars. Using a $15\,M_\odot$, $Z=0.02$ NuGrid model and post-processing with 3D-inspired mixing scenarios, it quantifies pre-explosive yields via the overproduction factor $OP_{R15}$ and compares them to explosive yields from both NuGrid and literature. It finds a broad range of pre-explosive yields across isotopes, with an average spread of $2.14$ dex and a $^{44}$Ti spread of $4.78$ dex, and identifies cases where pre-explosive $^{44}$Ti production can dominate explosive yields. The results underscore the importance of incorporating 3D hydrodynamic mixing during O-C mergers into stellar evolution and explosion models to accurately predict radioisotope production and interpret remnants like Cassiopeia A.

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 the pre-supernova O-C shell merger nucleosynthesis and if it can dominate the 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 $15~\mathrm{M}_\odot$ stellar model with mixing conditions corresponding to different 3D hydro mixing scenarios. Radioactive species produced in the O shell have a spread in their pre-explosive yields predictions across different 3D mixing scenarios of 2.14 dex on average. $^{44}\mathrm{Ti}$ has the largest spread of 4.78 dex. The pre-explosive production of $^{44}\mathrm{Ti}$ can be larger than the production of all massive star models in the NuGrid data set where $^{44}\mathrm{Ti}$ is dominated by the explosive nucleosynthesis contribution, as well all other massive star and supernova models. 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.

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

TL;DR

The study asks whether pre-supernova production of Ti during an O-C shell merger can rival or exceed explosive synthesis in massive stars. Using a , NuGrid model and post-processing with 3D-inspired mixing scenarios, it quantifies pre-explosive yields via the overproduction factor and compares them to explosive yields from both NuGrid and literature. It finds a broad range of pre-explosive yields across isotopes, with an average spread of dex and a Ti spread of dex, and identifies cases where pre-explosive Ti production can dominate explosive yields. The results underscore the importance of incorporating 3D hydrodynamic mixing during O-C mergers into stellar evolution and explosion models to accurately predict radioisotope production and interpret remnants like Cassiopeia A.

Abstract

The formation of 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 the pre-supernova O-C shell merger nucleosynthesis and if it can dominate the explosive supernova production of and other radioactive isotopes. We compare a range of observations and models of explosive yields to pre-explosive multi-zone mixing-burning nucleosynthesis simulations of an O-C shell merger in a stellar model with mixing conditions corresponding to different 3D hydro mixing scenarios. Radioactive species produced in the O shell have a spread in their pre-explosive yields predictions across different 3D mixing scenarios of 2.14 dex on average. has the largest spread of 4.78 dex. The pre-explosive production of can be larger than the production of all massive star models in the NuGrid data set where is dominated by the explosive nucleosynthesis contribution, as well all other massive star and supernova models. We conclude that quantitative predictions of and other radioactive species more broadly require an understanding of the 3D hydrodynamic mixing conditions present during the O-C shell merger.

Paper Structure

This paper contains 7 sections, 1 equation, 4 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Methods
  3. Results
  4. Nuclear production of $\mathrm{^{44}Ti}$ during O-C shell mergers
  5. Mixing and explosive yields of radioactive species
  6. Conclusions
  7. $\mathrm{^{44}Ti}$ Yields

Figures (4)

  • Figure 1: Mass fractions of radioactive isotopes in the $15\;\mathrm{\mathrm{M}_\odot}$$Z=0.02$ model from ritterNuGridStellarData2018 at the final time step before explosion. Both the $\mathrm{^{}O}$ shell and $\mathrm{^{}O}$-$\mathrm{^{}C}$ region are shaded to indicate their extent.
  • Figure 2: Chart of reactions between isotopes at $m = 1.6\;\mathrm{\mathrm{M}_\odot}$$[T = 2.494\times 10^{9}\;\mathrm{\mathrm{K}}]$ for the $50\times D_{\mathrm{3D{-}insp.}}$ mixing case with an ingestion rate of $4\times 10^{-3}\;\mathrm{\mathrm{M}_\odot \mathrm{s}^{-1}}$ at $t = 110\;\mathrm{\mathrm{s}}$. Both arrow colour and size indicate $\log_{10}(f_{ij})$, the reaction flux as defined in issaImpact3DMacro2025, and arrows point in the direction of the reaction.
  • Figure 3: Predicted yields of $\mathrm{^{44}Ti}$ compared to the $15\;\mathrm{\mathrm{M}_\odot}$$Z=0.02$ pre-explosive yields ($\mathrm{OP}_{\mathrm{R15}}$). The lower x-axis has the entrainment rates in $\mathrm{M}_\odot\mathrm{s}^{-1}$ and the upper x-axis has the quenched mixing cases summarized as (location of dip in $\mathrm{M}$$\mathrm{m}$, maximum extent of the dip in $\mathrm{c}\mathrm{m}^{2} \mathrm{s}^{-1}$). Colour indicates magnitude and size indicates distance from $\mathrm{OP}_{\mathrm{R15}}=1$. The explosive production of the $15\;\mathrm{\mathrm{M}_\odot}$$Z=0.02$ model is $\mathrm{OP}_{\mathrm{R15}}=0.49\;\mathrm{\, \mathrm{dex}}$.
  • Figure 4: $\mathrm{OP}_\mathrm{R15}$ for (1) inferred yields of $\mathrm{^{44}Ti}$ from supernova remnants observations (triangles with error bars) (2) explosive $\mathrm{^{44}Ti}$ yields of non-NuGrid models (blue circles) (3) explosive yields of all considered radioactive species from NuGrid models (small black stars) (4) explosive yields of the $15\;\mathrm{\mathrm{M}_\odot}$$Z=0.02$ NuGrid model (large black stars) (5) the maximum and minimum predicted pre-explosive yields for all scenarios (purple bars). Appendix \ref{['sec:appendix_explosive_yields']} provides the full list of citations.