3-D ELEMENTAL AND ISOTOPIC COMPOSITION OF PRESOLAR SILICON CARBIDES

Abstract

Thirteen presolar silicon carbide grains—three of supernova (SN) origin and ten of asymptotic giant branch (AGB) star origin—were examined with time‐of‐flight‐secondary ion mass spectrometry (TOF‐SIMS). The grains had been extracted from two different meteorites—Murchison and Tieschitz—using different acid residue methods. At high lateral resolution of ∼300 nm, isotopic and elemental heterogeneities within the micrometer‐sized grains were detected. The trace elemental abundances, when displayed in two‐element correlation plots, of Li, Mg, K, and Ca show a clear distinction between the two different meteoritic sources. The different concentrations might be attributed to differences of the host meteorites and/or of extraction methods whereas the stellar source seems to be less decisive. In one SN grain with ²⁶Mg‐enrichment from extinct ²⁶Al, the acid treatment, as part of the grain separation procedure, affected the Mg/Al ratio in the outer rim and therefore the inferred initial ²⁶Al/²⁷Al ratio. A second SN grain exhibits a lateral heterogeneity in ²⁶Al/²⁷Al, which either is due to residual Al‐rich contamination on the grain surface or to the condensation chemistry in the SN ejecta.