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.

Classical novae are stellar explosions occurring in binary systems, consisting of a white dwarf and a main sequence companion. Thermonuclear runaways on the surface of massive white dwarfs, consisting of oxygen and neon, are believed to reach peak temperatures of several hundred million kelvin. These temperatures are strongly correlated with the underlying white dwarf mass. The observational counterparts of such models are likely associated with outbursts that show strong spectral lines of neon in their shells (neon novae). The goals of this work are to investigate how useful elemental abundances are for constraining the peak temperatures achieved during these outbursts and determine how robust "nova thermometers" are with respect to uncertain nuclear physics input. We present updated observed abundances in neon novae and perform a series of hydrodynamic simulations for several white dwarf masses. We find that the most useful thermometers, N/are those with the steepest monotonic dependence on peak temperature. The sensitivity of these thermometers to thermonuclear reaction rate variations is explored using post-processing nucleosynthesis simulations. The ratios N/O, N/Al, O/Na, and Na/Al are robust, meaning they are minimally affected by uncertain rates. However, their dependence on peak temperature is relatively weak. The ratios O/S, S/Al, O/P, and P/Al reveal strong dependences on temperature and the poorly known 30 P(p,γ) 31 S rate. We compare our model predictions to neon nova observations and obtain the following estimates for the underlying white dwarf masses: 1.34-1.35 M ⊙ (V838 Her), 1.18-1.21 M ⊙ (V382 Vel), ≤1.3 M ⊙ (V693 CrA), ≤1.2 M ⊙ (LMC 1990#1), and ≤1.2 M ⊙ (QU Vul).

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.