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

TL;DR

This study uses AGB nucleosynthesis models with varied $^{13}$C-pocket structures to better match zirconium isotope measurements in presolar SiC grains, supporting a flat $^{13}$C profile hypothesis.

Contribution

It introduces a flat $^{13}$C-profile in AGB models to explain zirconium isotope data, improving agreement with presolar grain measurements.

Findings

Flat $^{13}$C profile predicts higher $^{92}$Zr/$^{94}$Zr ratios.

Models with flat $^{13}$C$ profile better match zirconium isotope data.

Supports recent proposals of flat $^{13}$C$ profile based on barium isotopes.

Abstract

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).