A Presolar Spinel Grain of Probable Nova

Introduction: Presolar grains from novae are exceedingly rare. A few SiC and graphite grains have been identified by large 13 C, 15 N, and 30 Si excesses [1, 2]. While some purported nova grains may have actually condensed in a supernova [3], some are undoubtedly nova condensates [4, 5]. Except in rare cases, the material ejected in nova explosions is O-rich, and it remains a puzzle why to date only carbonaceous phases, with one possible exception [6], have been identified. Here we report the discovery of a presolar spinel grain with a likely nova origin. Experimental: The " CG " residue of Murray, prepared by physical and chemical separation [7] and consisting of high concentrations of spinel grains (diameter ~0.5μm), was scanned for O-anomalous grains with an automated measurement technique recently developed for the NanoSIMS [8]. Grain C4-8 was not identified by the particle definition software, but was recognized as an 17 O hotspot in an ion image taken during the automated surveys. High-resolution SEM images confirmed that it was surrounded by multiple grains. Subsequent removal of surrounding isotopically normal material [9] and manual measurement of 16,17,18 O revealed the grain to be extremely enriched in 17 O. Following O isotopic analysis, 24,25,26 Mg + and 27 Al + were measured in multicollection mode with an O – primary beam in a separate measurement session.