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
Year: 2026
Type: article
Abstract: 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 (≳0.1), due to 20 Ne depletion and production of 36 Ar and 38 Ar, while lower ratios are obtained from nonmerger 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 ∼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 COS I 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.
Institutions: University of California, Berkeley, University of Perugia, Astronomical Observatory of Rome, Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, National Institute for Astrophysics, Los Alamos National Laboratory, University of Manitoba, University of Bayreuth
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Funders: National Science Foundation, U.S. Department of Energy, University of Victoria, University of Hull, European Commission, Canada Research Chairs, Magyar Tudományos Akadémia, Nemzeti Kutatási Fejlesztési és Innovációs Hivatal, Office of Science, National Nuclear Security Administration, Natural Sciences and Engineering Research Council of Canada, Office of International Science and Engineering, Nuclear Physics, Los Alamos National Laboratory, Triad National Security
Awards: G1017065088, G1214995468, G1279347439, G1527848044, NUCLEAR PHYSICS AND ASTROPHYSICS THEORY AT UC BERKELEY, G1795988247, G2014318462, G2227819465, G2286656435, G2290926408, G2690551473, G2769614280, G2890494086, G3223808969, AccelNet-WOU: International Research Network for Nuclear Astrophysics (IReNA), G4203880831, G4381829875, G5585190046, G5855085320, G5912852498, G604949671, G6410514744, G6563880843, G6767015034, Chemical Elements as Tracers of the Evolution of the Cosmos - Infrastructures for Nuclear Astrophysics, G70659677, G7825530859, G7843896931, G7854219128, G8195235826, G949321373
OpenAlex ID: W7160859560