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

TL;DR

This study provides the most precise measurement to date of the 64.5 keV resonance strength in the $^{17}$O(p,$ extalpha$)$^{14}$N reaction, significantly refining astrophysical reaction rates relevant to stellar nucleosynthesis.

Contribution

It presents a new direct measurement of the resonance strength at LUNA, improving accuracy and reducing background noise, leading to revised reaction rates in astrophysical models.

Findings

Resonance strength measured as 10.0 ± 1.4_stat ± 0.7_syst neV.

Proton partial width is about twice previous estimates.

Reaction rate increase impacts $^{17}$O/$^{16}$O ratio predictions.

Abstract

The $^{17}$O(p,$\alpha$)$^{14}$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 $E_{\rm R}~=~64.5$~keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics accelerator has led to the most accurate value to date, $\omega\gamma = 10.0 \pm 1.4_{\rm stat} \pm 0.7_{\rm syst}$~neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at $E_{\rm x} = 5672$~keV in $^{18}$F is $\Gamma_{\rm p} = 35 \pm 5_{\rm stat} \pm 3_{\rm syst}$~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,$\alpha$)$^{14}$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.