Production of heavy $α$-elements and $^{44}$Ti in Cas A: comparison to abundances from 1D core-collapse supernova models and evidence for Carbon-Oxygen shell mergers
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| Format: | Preprint |
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2026
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| _version_ | 1866913130303455232 |
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| author | Boccioli, Luca Roberti, Lorenzo Fryer, Chris L Safi-Harb, Samar Jones, Samuel Pignatari, Marco |
| author_facet | Boccioli, Luca Roberti, Lorenzo Fryer, Chris L Safi-Harb, Samar Jones, Samuel Pignatari, Marco |
| contents | The merger between the carbon (C) and oxygen (O) shells hours to days before the collapse of a massive star significantly changes its nucleosynthesis, which is reflected in the elemental ratios observed in supernova remnants (SNRs). We present a nucleosynthesis study of $^{44}$Ti production in core-collapse supernovae (CCSNe), highlighting large silicon (Si), sulfur (S), calcium (Ca), and, most importantly, argon (Ar) to neon (Ne) ratios as diagnostics for carbon-oxygen (C--O) shell mergers. We compare yields from eight different sets of CCSNe models to observations of Cassiopeia A (Cas A), and show that C--O shell mergers are consistently the models that best match X-ray and infrared observations. These models produce high Ar/Ne ratios ($\gtrsim 0.1$), due to $^{20}$Ne depletion and production of $^{36}$Ar and $^{38}$Ar, while lower ratios are obtained from non-merger cases. Based on the Ar/Ne diagnostic, we compare the range of expected $^{44}$Ti produced by C--O shell mergers, which is up to $\sim 20 - 30 \%$ of the overall $^{44}$Ti, but expected to be located outside the reverse shock. Based on the sets of models considered, the photon flux expected from the $^{44}$Ti synthesized in the C--O shell merger in Cas A is below the $NuSTAR$ and $COSI$ detection limits, compatible with current limits locating most of the $^{44}$Ti interior to the reverse shock, but might be detectable from proposed missions like $ASCENT$. Finally, for the SNR of 1987A, a dominant C--O merger origin of the observed $^{44}$Ti is unlikely based on the observed redshift in its $^{44}$Ti line. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_24758 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Production of heavy $α$-elements and $^{44}$Ti in Cas A: comparison to abundances from 1D core-collapse supernova models and evidence for Carbon-Oxygen shell mergers Boccioli, Luca Roberti, Lorenzo Fryer, Chris L Safi-Harb, Samar Jones, Samuel Pignatari, Marco High Energy Astrophysical Phenomena Astrophysics of Galaxies Solar and Stellar Astrophysics The merger between the carbon (C) and oxygen (O) shells hours to days before the collapse of a massive star significantly changes its nucleosynthesis, which is reflected in the elemental ratios observed in supernova remnants (SNRs). We present a nucleosynthesis study of $^{44}$Ti production in core-collapse supernovae (CCSNe), highlighting large silicon (Si), sulfur (S), calcium (Ca), and, most importantly, argon (Ar) to neon (Ne) ratios as diagnostics for carbon-oxygen (C--O) shell mergers. We compare yields from eight different sets of CCSNe models to observations of Cassiopeia A (Cas A), and show that C--O shell mergers are consistently the models that best match X-ray and infrared observations. These models produce high Ar/Ne ratios ($\gtrsim 0.1$), due to $^{20}$Ne depletion and production of $^{36}$Ar and $^{38}$Ar, while lower ratios are obtained from non-merger cases. Based on the Ar/Ne diagnostic, we compare the range of expected $^{44}$Ti produced by C--O shell mergers, which is up to $\sim 20 - 30 \%$ of the overall $^{44}$Ti, but expected to be located outside the reverse shock. Based on the sets of models considered, the photon flux expected from the $^{44}$Ti synthesized in the C--O shell merger in Cas A is below the $NuSTAR$ and $COSI$ detection limits, compatible with current limits locating most of the $^{44}$Ti interior to the reverse shock, but might be detectable from proposed missions like $ASCENT$. Finally, for the SNR of 1987A, a dominant C--O merger origin of the observed $^{44}$Ti is unlikely based on the observed redshift in its $^{44}$Ti line. |
| title | Production of heavy $α$-elements and $^{44}$Ti in Cas A: comparison to abundances from 1D core-collapse supernova models and evidence for Carbon-Oxygen shell mergers |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2603.24758 |