$^{22}$Ne and $^{23}$Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for $^{22}$Ne(p,$\gamma$)$^{23}$Na

TL;DR

This study assesses how the new LUNA nuclear reaction rate for $^{22}$Ne$(p, extgamma)^{23}$Na reduces uncertainties in the chemical yields of intermediate-mass stars, especially in the context of globular cluster abundance patterns.

Contribution

It provides updated stellar evolution models incorporating the new LUNA rate, significantly reducing nuclear uncertainties in $^{22}$Ne and $^{23}$Na ejecta and analyzing implications for globular cluster chemical anomalies.

Findings

Nuclear uncertainties in Na and Ne ejecta are greatly reduced.

Remaining uncertainties are mainly due to stellar evolution processes.

Implications for the origin of O-Na anti-correlation in globular clusters.

Abstract

We investigate the impact of the new LUNA rate for the nuclear reaction $^{22}$Ne$(p,\gamma)^{23}$Na on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range $3.0\,M_{\odot} - 6.0\,M_{\odot}$, and metallicities $Z_{\rm i}=0.0005$, $Z_{\rm i}=0.006$, and $Z_{\rm i} = 0.014$. We find that the new LUNA measures have much reduced the nuclear uncertainties of the $^{22}$Ne and $^{23}$Na AGB ejecta, which drop from factors of $\simeq 10$ to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of $^{23}$Na, the uncertainties that still affect the $^{22}$Ne and $^{23}$Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available.