Constraining the S factor of N15(p,γ)O16 at astrophysical energies

The N15(p,γ)O16 reaction represents a breakout reaction linking the first and second cycles of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances, at E_p=338 and 1028 keV, and a direct capture contribution to the ground state of O16. Interference effects between these contributions both in the low-energy region (E_p<338 keV) and between the two resonances (338<E_p<1028 keV) can dramatically affect the extrapolation to energies of astrophysical interest. To facilitate a reliable extrapolation, the N15(p,γ)O16 reaction has been remeasured covering the energy range from E_p=1800 keV down to 130 keV. The results have been analyzed in the framework of a multilevel R-matrix theory and an S(0) value of 39.6 keV b has been found.