Improved Direct Measurement of the 64.5 keV Resonance Strength in theO17(p,α)N14Reaction at LUNA

The O17(p,α)N14 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 O17 and F18, which can provide constraints on astrophysical models. A new direct determination of the ER=64.5 keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator has led to the most accurate value to date ωγ=10.0±1.4stat±0.7syst neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at Ex=5672 keV in F18 is Γp=35±5stat±3syst neV. This width is about a factor of 2 higher than previously estimated, thus leading to a factor of 2 increase in the O17(p, α)N14 reaction rate at astrophysical temperatures relevant to shell hydrogen burning in red giant and asymptotic giant branch stars. The new rate implies lower O17/O16 ratios, with important implications on the interpretation of astrophysical observables from these stars.