²²Ne and²³Na ejecta from intermediate-mass stars: the impact of the new LUNA rate for²²Ne(<i>p</i>, γ)²³Na

Abstract

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