High Resolution Study of ${}^{40}$Ca to Constrain Potassium Nucleosynthesis in NGC 2419

Abstract

The globular cluster NGC 2419 was the first to exhibit a Mg-K anticorrelation, linked to hydrogen burning at temperatures between 80-260 MK. However, the key K-destroying reaction, ${}^{39}\mathrm{K}(p,{\hat{I}}^3{)}^{40}\mathrm{Ca}$, has a large rate uncertainty in this range. We significantly constrain this rate with a high resolution ${}^{39}\mathrm{K}{(}^3\mathrm{He},d{)}^{40}\mathrm{Ca}$ study. We resolve the E${}_{\text{r}}^{\text{c.m.}}=154$ keV resonance in ${}^{39}\mathrm{K}+p$ for the first time, increasing the previous rate by up to a factor 13 and reducing its $1\ddot{I}ƒ$ width by up to a factor of 42. Reaction network calculations for NGC 2419 suggest that this could lower temperatures needed to reproduce the Mg-K anticorrelation.