Isotopic ratios for C, N, Si, Al, and Ti in C-rich presolar grains from massive stars

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 C-12, Si-28, and Ti-44. 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 Si-28 and Ti-44 isotopic abundances in grains without assuming mixing with O-rich CCSN ejecta. The most Si-28-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 Ti-44/Ti-48 and Ti-49/Ti-48 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 Al-26 to reproduce the Al-26/Al-27 measurements of most SiC-X and LD graphites. In both cases, the highest Al-26/Al-27 ratio is obtained with H still present at X-H approximate to 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.

Automated summary

In this study, isotopic abundances of C, N, Al, Si, and Ti measured in presolar grains were compared with predictions from 21 CCSN models. The research found that high energy models favor the formation of a C/Si zone enriched in C-12, Si-28, and Ti-44.