Silicon and Carbon Isotopic Ratios in AGB Stars: SiC Grain Data, Models, and the Galactic Evolution of the Si Isotopes

Presolar SiC grains of the mainstream, Y, and Z type are believed to come from carbon stars. We compared their C and Si isotopic ratios with theoretical models for the envelope compositions of AGB stars. Two sets of models (FRANEC and Monash) use a range