Carbon, Nitrogen, and Silicon Isotopic Ratios in Kjg Presolar Sic Grains from Murchison

Introduction: SiC is the best-studied type of presolar grains [1]. Thousands of individual grains have been measured for their C and Si isotopic compositions [2-4] and many of these have been measured for additional isotopic systems, as well. Despite this wealth of data and the fact that Ti is one of the most abundant trace elements in SiC, only approximately 110 SiC grains have had their Ti isotopic compositions determined [3,5-8] and of these, most suffer from selection effects. Specifically, the Ti data for mainstream SiC, thought to have formed in the outflows of lowmass (1–3MO) C-rich Asymptotic Giant Branch (AGB) stars [9], have not been obtained from a representative sample of the larger population as a whole. The grains analyzed have been chosen either for their high Ti concentrations [5] or their large Si and Si excesses [3].