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

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 He, Ne, Ne or Ne, or a combination thereof. We report the first detection of Ne from an individual presolar graphite grain and the first detection of He and Ne 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 Ne 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 Ne and C/C <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 Ne and Ne, and a further grain with Ne and Ne 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. 2011 Elsevier Ltd. All rights reserved.