Speaker
Description
Current stellar nucleosynthesis models fail to reproduce the measured isotopic abundances in group 2 oxygen-rich presolar grains, which are characterized by large ${}^{18}$O depletions. It was proposed that cool bottom processing in low-mass AGB stars is responsible for the observed isotopic abundances. We modeled cool-bottom processing during the RGB and the AGB of $1.2M_{\odot}$ stars to predict surface ${}^{18}$O/${}^{16}$O, ${}^{17}$O/${}^{16}$O, and ${}^{26}$Al/${}^{27}$Al ratios. Effective secular mixing must work against the steep mean molecular weight ($\mu$) gradient at the bottom of the radiative zone below the convective envelope to overcome a net increase in $\mu$ on the order of $0.01\%$ to recreate observed isotopic ratios. Sensitivity tests in which ${}^{18}$O$(p,\alpha){}^{15}$N and ${}^{16}$O$(p,\gamma){}^{17}$F were varied using reaction rate of factors of 10/0.1 and 1.4/0.71 respectively suggest that nuclear physics input is an important factor in model-grain comparison. This work shows that a secular cool-bottom mixing model that preserves stratification is a viable origin mechanism of the isotopic ratios observed in grains. We will also present an analysis of the surface ${}^{26}$Mg/${}^{24}$Mg, and ${}^{25}$Mg/${}^{24}$Mg ratios, $2M_{\odot}$ and $3M_{\odot}$ stars, and Monte Carlo impact studies on a range of reactions using current experimental uncertainties.
