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 (4)He, (20)Ne, (21)Ne or (22)Ne, or a combination thereof. We report the first detection of (21)Ne from an individual presolar graphite grain and the first detection of (4)He and (20)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 (22)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 (20)Ne and (12)C/(13)C < 10 are consistent with condensation and Ne acquisition in a similar to 80:20 mixture of material from the H envelope and He/N zone. The isotopic ratios of a single grain with (21)Ne and (22)Ne, and a further grain with (20)Ne and (22)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. (C) 2011 Elsevier Ltd. All rights reserved.