Graphite grains in supernova ejecta – Insights from a noble gas study of 91 individual KFC1 presolar graphite grains from the Murchison meteorite

Abstract

We have measured helium and neon concentrations, elemental and isotopic ratios of 91 individual presolar graphite grains from the KFC1 density separate of the Murchison meteorite. Eleven grains contain measurable amounts of either 4He, 20Ne, 21Ne or 22Ne, or a combination thereof. We report the first detection of 21Ne from an individual presolar graphite grain and the first detection of 4He and 20Ne in individual KFC1 graphite grains. Six of the gas-rich grains originate from asymptotic giant branch (AGB) stars, while another five are likely derived from core-collapse supernovae. The mono-isotopic 22Ne detected in one supernova grain is either radiogenic and compatible with condensation in the O/Ne zone, or nucleosynthetic and derived from the He/C zone. Two grains with 20Ne and 12C/ 13C <10 are consistent with condensation and Ne acquisition in a ∼80:20 mixture of material from the H envelope and He/N zone. The isotopic ratios of a single grain with 21Ne and 22Ne, and a further grain with 20Ne and 22Ne are compatible with condensation and Ne acquisition in the C/O zone. We discuss the implications of our study on the understanding of processes in supernova ejecta.