Indirect measurement of the 27Al(p,α)24Mg and 27Al(p,γ)28Si cross sections and astrophysical implications

Abstract

In astrophysics, the presence of ²⁶Al is vital for investigating nucleosynthesis within the Milky Way and the rate of Galactic core-collapse supernovae. Detection techniques utilize γ-ray lines and compare ²⁶Mg excess with the prevalent Mg isotope in meteorites. Hence, stable isotopes ²⁷Al and ²⁴Mg are crucial, and the MgAl cycle impacting aluminum and magnesium synthesis must be thoroughly examined. Recent observations uncover complexities in stellar groups, whose comprehension may also improve with tighter constraints on the MgAl cycle's closure. The ²⁷Al(${p,\alpha )}^{24}$Mg and ²⁷Al(${p,\gamma )}^{28}$Si reactions, primary ²⁷Al destruction pathways, are pivotal to these models. Given uncertainties, the Trojan Horse Method is used, enabling precise spectroscopy of the compound nucleus ²⁸Si. This provides essential cross section data within the relevant astrophysical energy range. The indirect measurement via the ²H(²⁷Al, $\alpha {}^{24}$Mg)n reaction allowed for evaluating the 84.3 keV resonance's contribution and setting upper limits on adjacent resonances. This research examines the THM recommended rate's influence on intermediate-mass asymptotic giant branch stars, demonstrating a significant rise in surface aluminum abundance in lower masses due to changes in fusion cross sections, while ²⁴Mg remains mostly unchanged.