A New Reaction Rate of the 27Al(p,γ)28Si Reaction Based on Indirect Low-energy Cross-section Measurements

Abstract

The Mg–Al cycle is characteristic of the high-temperature (T ∼ 0.055 GK) H-burning of evolved stars and their nucleosynthesis. A proper comprehension of this reaction network can help in solving debated questions such as the occurrence of anticorrelation in Mg–Al abundances in globular clusters. Recent high-resolution surveys have shown that such an anticorrelation may hide the existence of multiple stellar populations and that the relative abundances of Mg isotopes may not be correlated with Al. Proton-induced reactions on 27Al play a key role in this respect, in particular the interplay between the (p, α) and (p, γ) channels, determining the closure (or not) of the Mg–Al cycle. Presently, the situation is still debated owing to the large uncertainty affecting existing experimental nuclear data. A recent indirect measurement indicates a further reduction in the 27Al(p, α)24Mg reaction rate with respect to the ones commonly adopted in astrophysical models. In the present work, we update the 27Al(p,γ)28Si reaction rate based on the same indirect measurement results. In the case of AGB stars experiencing hot bottom burning, the revised rate would lead to a ∼35% increase in 27Al abundance with respect to what is presently foreseen, with interesting astrophysical consequences.