Hydrogen burning of the oxygen isotopes takes place in low-mass stars, AGB stars, and classical novae. Observations of oxygen elemental and isotopic abundances in stellar spectra or in presolar grains provide strong constraints for stellar models if reliable thermonuclear reaction rates for hydrogen burning of oxygen are available. We present the results of a new measurement of the 17 O(p,γ) 18 F reaction in the laboratory bombarding energy range of 170−530 keV. The measurement is performed with significantly higher beam intensities (I max ≈ 2 mA) compared to previous work and by employing a sophisticated γ-ray coincidence spectrometer. We measured the cross section at much lower energies than previous in-beam experiments. We also apply a novel data analysis technique that is based on the decomposition of different contributions to the measured pulseheight spectrum. Our measured strengths of the low energy resonances amount to ωγ pres (193 keV) = (1.86 ± 0.13) × 10 −6 eV and ωγ pres (518 keV) = (13.70 ± 0.96) × 10 −3 eV. For the direct capture S-factor at zero energy, we find a value of S pres DC (0) = 4.82 ± 0.41 keVb. We also present new thermonuclear rates for the 17 O+p reactions, taking into account all consistent results from previous measurements.

The 22 Ne(p,γ) 23 Na reaction is one of the most uncertain reactions in the NeNa cycle and plays a crucial role in the creation of 23 Na, the only stable Na isotope. Uncertainties in the low-energy rates of this and other reactions in the NeNa cycle lead to ambiguities in the nucleosynthesis predicted from models of thermally pulsing AGB stars. This in turn complicates the interpretation of anomalous Na-O trends in globular cluster evolutionary scenarios. (2015) and is attributed to the interplay between the 23 Na(p,α) 20 Ne and 20 Ne(p,γ) 21 Na reactions, both of which remain fairly uncertain at the relevant temperature range.