The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains

We present postprocess AGB nucleosynthesis models with different ${}^{13}$C-pocket internal structures to better explain zirconium isotope measurements in mainstream presolar SiC grains by Nicolussi et al. (1997) and Barzyk et al. (2007). We show that higher-than-solar ${}^{92}$Zr/${}^{94}$Zr ratios can be predicted by adopting a ${}^{13}$C-pocket with a flat ${}^{13}$C profile, instead of the previous decreasing-with-depth ${}^{13}$C profile. The improved agreement between grain data for zirconium isotopes and AGB models provides additional support for a recent proposal of a flat ${}^{13}$C profile based on barium isotopes in mainstream SiC grains by Liu et al. (2014).