First direct measurement of the 64.5 keV resonance strength in $^{17}$O(p,$\gamma$)$^{18}$F reaction

TL;DR

This paper reports the first direct measurement of the 64.5 keV resonance strength in the $^{17}$O(p,$$)$^{18}$F reaction, crucial for understanding stellar nucleosynthesis in the CNO cycle.

Contribution

It provides the first direct measurement of the resonance strength at 64.5 keV and the direct capture contribution, improving nuclear reaction rate data relevant for astrophysics.

Findings

Resonance strength measured as (30 ± 6 stat ± 2 syst) peV.

Resonance strength is about twice the previous literature values.

Results support existing models of oxygen isotopic ratios in stars.

Abstract

The CNO cycle is one of the most important nuclear energy sources in stars. At temperatures of hydrostatic H-burning (20 MK $<$ T $<$ 80 MK) the $^{17}$O(p,$\gamma$)$^{18}$F reaction rate is dominated by the poorly constrained 64.5~keV resonance. Here we report on the first direct measurements of its resonance strength and of the direct capture contribution at 142 keV, performed with a new high sensitivity setup at LUNA. The present resonance strength of $\omega\gamma_{(p, \gamma)}$\textsuperscript{bare} = (30 $\pm$ 6\textsubscript{stat} $\pm$ 2\textsubscript{syst})~peV is about a factor of 2 higher than the values in literature, leading to a $\Gamma$\textsubscript{p}\textsuperscript{bare} = (34 $\pm$ 7\textsubscript{stat} $\pm$ 3\textsubscript{syst})~neV, in agreement with LUNA result from the (p,$\alpha$) channel. Such agreement strengthen our understanding of the oxygen isotopic ratios measured in red giant stars and in O-rich presolar grains.