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The NO cycle takes place in the deepest layer of a H-burning core or shell,when the temperature exceeds T {\simeq} 30 {\cdot} 106 K. The O depletionobserved in some globular cluster giant stars, always associated with a Naenhancement, may be due to either a deep mixing during the RGB (red giantbranch) phase of the star or to the pollution of the primordial gas by an earlypopulation of massive AGB (asymptotic giant branch) stars, whose chemicalcomposition was modified by the hot bottom burning. In both cases, the NO cycleis responsible for the O depletion. The activation of this cycle depends on therate of the 15N(p,{\gamma})16O reaction. A precise evaluation of this reactionrate at temperatures as low as experienced in H-burning zones in stellarinteriors is mandatory to understand the observed O abundances. We present anew measurement of the 15N(p,{\gamma})16O reaction performed at LUNA coveringfor the first time the center of mass energy range 70-370 keV, whichcorresponds to stellar temperatures between 65 {\cdot} 106 K and 780 {\cdot}106K. This range includes the 15N(p,{\gamma})16O Gamow-peak energy of explosiveH-burning taking place in the external layer of a nova and the one of the hotbottom burning (HBB) nucleosynthesis occurring in massive AGB stars. With thepresent data, we are also able to confirm the result of the previous R-matrixextrapolation. In particular, in the temperature range of astrophysicalinterest, the new rate is about a factor of 2 smaller than reported in thewidely adopted compilation of reaction rates (NACRE or CF88) and theuncertainty is now reduced down to the 10% level.

Revision of the 15N(p,{\gamma})16O reaction rate and oxygen abundance in H-burning zones