Improved Direct Measurement of the 64.5 keV Resonance Strength in the 17O(p,a)14N Reaction at LUNA

Abstract

The ${}^{17}$O(p,$\hat{I}\pm$)${}^{14}$N reaction plays a key role in various astrophysical scenarios, from asymptotic giant branch stars to classical novae. It affects the synthesis of rare isotopes such as ${}^{17}$O and ${}^{18}$F, which can provide constraints on astrophysical models. A new direct determination of the $E_{\mathrm{R}}=64.5$~keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics accelerator has led to the most accurate value to date, $\ddot{I}‰{\hat{I}}^3=10.0\pm 1.4_{\mathrm{stat}}\pm 0.7_{\mathrm{syst}}$~neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at $E_{\mathrm{x}}=5672$~keV in ${}^{18}$F is $\hat{I}{“}_{\mathrm{p}}=35\pm 5_{\mathrm{stat}}\pm 3_{\mathrm{syst}}$~neV. This width is about a factor of 2 higher than previously estimated thus leading to a factor of 2 increase in the ${}^{17}$O(p,$\hat{I}\pm$)${}^{14}$N reaction rate at astrophysical temperatures relevant to shell hydrogen-burning in red giant and asymptotic giant branch stars. The new rate implies lower ${}^{17}$O/${}^{16}$O ratios, with important implications on the interpretation of astrophysical observables from these stars.