STELLAR ORIGINS OF EXTREMELY {sup 13}C- AND {sup 15}N-ENRICHED PRESOLAR SIC GRAINS: NOVAE OR SUPERNOVAE?

• Published in: The Astrophysical journal Vol. 820; no. 2
• Main Authors: Liu, Nan, Nittler, Larry R., Alexander, Conel M. O’D., Wang, Jianhua, Pignatari, Marco, José, Jordi, Nguyen, Ann
• Format: Journal Article
• Language: English
• Published: United States 01.04.2016
• Subjects: ALUMINIUM 26; ALUMINIUM 27; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON 12; CARBON 13; COSMIC PROTONS; HYDROGEN BURNING; INTERSTELLAR GRAINS; METEORITES; METEOROIDS; NITROGEN 14; NITROGEN 15; NOVAE; NUCLEAR PHYSICS AND RADIATION PHYSICS; NUCLEOSYNTHESIS; SILICON 29; SILICON 30; SILICON CARBIDES; SULFUR 32; SULFUR 34; SUPERNOVAE
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/0004-637X/820/2/140

Extreme excesses of {sup 13}C ({sup 12}C/{sup 13}C < 10) and {sup 15}N ({sup 14}N/{sup 15}N < 20) in rare presolar SiC grains have been considered diagnostic of an origin in classical novae, though an origin in core collapse supernovae (CCSNe) has also been proposed. We report C, N, and Si isotope data for 14 submicron- to micron-sized {sup 13}C- and {sup 15}N-enriched presolar SiC grains ({sup 12}C/{sup 13}C < 16 and {sup 14}N/{sup 15}N < ∼100) from Murchison, and their correlated Mg–Al, S, and Ca–Ti isotope data when available. These grains are enriched in {sup 13}C and {sup 15}N, but with quite diverse Si isotopic signatures. Four grains with {sup 29,30}Si excesses similar to those of type C SiC grains likely came from CCSNe, which experienced explosive H burning occurred during explosions. The independent coexistence of proton- and neutron-capture isotopic signatures in these grains strongly supports heterogeneous H ingestion into the He shell in pre-supernovae. Two of the seven putative nova grains with {sup 30}Si excesses and {sup 29}Si depletions show lower-than-solar {sup 34}S/{sup 32}S ratios that cannot be explained by classical nova nucleosynthetic models. We discuss these signatures within the CCSN scenario. For the remaining five putative nova grains, both nova and supernova origins are viable because explosive H burning in the two stellar sites could result in quite similar proton-capture isotopic signatures. Three of the grains are sub-type AB grains that are also {sup 13}C enriched, but have a range of higher {sup 14}N/{sup 15}N. We found that {sup 15}N-enriched AB grains (∼50 < {sup 14}N/{sup 15}N < ∼100) have distinctive isotopic signatures compared to putative nova grains, such as higher {sup 14}N/{sup 15}N, lower {sup 26}Al/{sup 27}Al, and lack of {sup 30}Si excess, indicating weaker proton-capture nucleosynthetic environments.