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ABSTRACT Certain types of silicon carbide (SiC) grains, e.g. SiC-X grains, and low density (LD) graphites are C-rich presolar grains that are thought to have condensed in the ejecta of core-collapse supernovae (CCSNe). In this work, we compare C, N, Al, Si, and Ti isotopic abundances measured in presolar grains with the predictions of 21 CCSN models. The impact of a range of SN explosion energies is considered, with the high energy models favouring the formation of a C/Si zone enriched in 12C, 28Si, and 44Ti. Eighteen of the 21 models have H ingested into the He-shell and different abundances of H remaining from such H-ingestion. CCSN models with intermediate to low energy (that do not develop a C/Si zone) cannot reproduce the 28Si and 44Ti isotopic abundances in grains without assuming mixing with O-rich CCSN ejecta. The most 28Si-rich grains are reproduced by energetic models when material from the C/Si zone is mixed with surrounding C-rich material, and the observed trends of the 44Ti/48Ti and 49Ti/48Ti ratios are consistent with the C-rich C/Si zone. For the models with H-ingestion, high and intermediate explosion energies allow the production of enough 26Al to reproduce the 26Al/27Al measurements of most SiC-X and LD graphites. In both cases, the highest 26Al/27Al ratio is obtained with H still present at XH ≈ 0.0024 in He-shell material when the SN shock is passing. The existence of H in the former convective He-shell points to late H-ingestion events in the last days before massive stars explode as a supernova.
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New Constraints for Supernova Models from Presolar Silicon Carbide X Grains with Very High 26 Al/ 27 Al Ratios
Abstract We report C, N, Mg-Al, Si, and S isotope data of six 1–3μm-sized SiC grains of Type X from the Murchison CM2 chondrite, believed to have formed in the ejecta of core-collapse supernova (CCSN) explosions. Their C, N, and Si isotopic compositions are fully compatible with previously studied X grains. Magnesium is essentially monoisotopic26Mg which gives clear evidence for the decay of radioactive26Al. Inferred initial26Al/27Al ratios are between 0.6 and 0.78 which is at the upper end of previously observed ratios of X grains. Contamination with terrestrial or solar system Al apparently is low or absent, which makes the X grains from this study particularly interesting and useful for a quantitative comparison of Al isotope data with predictions from supernova models. The consistently high26Al/27Al ratios observed here may suggest that the lower26Al/27Al ratios of many X grains from the literature are the result of significant Al contamination and in part also of an improper quantification of26Al. The real dispersion of26Al/27Al ratios in X grains needs to be explored by future studies. The high observed26Al/27Al ratios in this work provide a crucial constraint for the production of26Al in CCSN models. We explored different CCSN models, including both “classical” and H ingestion CCSN models. It is found that the classical models cannot account for the high26Al/27Al ratios observed here; in contrast, H ingestion models are able to reproduce the26Al/27Al ratios along with C, N, and Si isotopic ratios reasonably well.
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- Award ID(s):
- 1927130
- PAR ID:
- 10394740
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 943
- Issue:
- 2
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L22
- Size(s):
- Article No. L22
- Sponsoring Org:
- National Science Foundation
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