New NanoSIMS Multielement Isotope Data Reveal CO Novae As Key Sources Of 13C-rich Presolar Silicon Carbide Grains

Abstract

We present new multielement NanoSIMS isotopic measurements (C, N, Si, Mg-Al, Ti, and Ni) for four putative nova SiC grains and 79 AB SiC grains from the Murchison meteorite to reassess their stellar origins. High-resolution imaging and a revised Mg/Al relative sensitivity factor for SiC yield substantially improved 26Al/27Al ratios and the most reliable multielement characterization to date for 13C-rich presolar SiC grains. To interpret these data, we computed an expanded suite of hydrodynamic CO, ONe, and recurrent nova models spanning a range of white-dwarf masses and pre-enrichment parameters. When all isotopic systems are considered together (C, N, Mg-Al, Si, Ti, and Ni), the CO nova models provide the closest and most self-consistent match to both the putative nova grains and the subset of AB grains lacking s-process signatures. CO novae of low- to intermediate-mass naturally reproduce the observed 14N/15N-26Al/27Al trend, the Si isotope compositions of AB grains which dominantly reflect Galactic chemical evolution (GCE), and the mild Si isotope shifts in putative nova grains relative to the GCE trend defined by AB grains. In contrast, ONe and recurrent nova models fail multiple isotopic constraints simultaneously. These results demonstrate that low- to intermediate-mass CO novae (0.6-1.0 Msun) are the most plausible stellar sources of 13C-rich SiC dust lacking s-process signatures (1-2\% of all presolar SiC), and they establish a multielement, model-anchored framework for quantifying nova contributions to the dust reservoir in the interstellar medium.