Evidence for a range of metallicities in the parent stars of presolar SiC grains

The majority of presolar SiC grains present in primitive meteorites have been identified to condense from the winds of C-rich AGB stars. The Si isotopic ratios of three types (mainstream, Y and Z grains) can be used to obtain information about the metallicity of their parent stars. Single grain data and results from nucleosynthetic calculations indicate that mainstream grains are from stars of close-to-solar metallicity, grains of type Y from stars with metallicity Z ≈ 0.01 and grains of type Z from stars with Z ≈ 0.006. These results in turn suggest that the Galactic evolution of the ^29,30Si/²⁸Si ratios shortly before and at solar system formation was slower than previously believed.