Stellar origin of 15N-rich presolar SiC grains of type AB: supernovae with explosive hydrogen burning

TL;DR

This study analyzes isotopic compositions of presolar SiC grains from meteorites, revealing their supernova origins with evidence of explosive hydrogen burning and neutron-capture processes, and introduces a new classification of AB grains based on nitrogen isotopes.

Contribution

It provides the first combined S and Ti isotopic data for AB grains, linking their isotopic signatures to supernova models with hydrogen ingestion in the He/C zones.

Findings

AB grains show distinct 15N and 26Al excesses correlating with supernova models.

Presence of 32S and 50Ti excesses suggests neutron-capture nucleosynthesis.

AB1 and C2 grains likely originate from supernovae with hydrogen ingestion.

Abstract

We report C, N, and Si isotopic data for 59 highly 13C-enriched presolar submicron- to micron-sized SiC grains from the Murchison meteorite, including eight putative nova grains (PNGs) and 29 15N-rich (14N/15N<=solar) AB grains, and their Mg-Al, S, and Ca-Ti isotope data when available. These 37 grains are enriched in 13C, 15N and 26Al with the PNGs showing more extreme enhancements. The 15N-rich AB grains show systematically higher 26Al and 30Si excesses than the 14N-rich AB grains. Thus, we propose to divide the AB grains into groups 1 (14N/15N<solar) and 2 (14N/15N>=solar). For the first time, we have obtained both S and Ti isotopic data for five AB1 grains and one PNG, and found 32S and/or 50Ti enhancements. Interestingly, one AB1 grain had the largest 32S and 50Ti excesses, strongly suggesting a neutron-capture nucleosynthetic origin of the 32S excess and thus the initial presence of radiogenic 32Si (t1/2=153 yr). More importantly, we found that the 15N and 26Al excesses of AB1 grains form a trend that extends to the region in the N-Al isotope plot occupied by C2 grains, strongly indicating a common stellar origin for both AB1 and C2 grains. Comparison of supernova models with the AB1 and C2 grain data indicates that these grains came from SNe that experienced H ingestion into the He/C zones of their progenitors.