Volume 533, September 2011
|Number of page(s)||6|
|Section||Atomic, molecular, and nuclear data|
|Published online||29 August 2011|
Revision of the 15N(p, γ)16O reaction rate and oxygen abundance in H-burning zones
Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova, via
2 Dipartimento di Scienze della Terra, Università di Siena, 53100 Siena; and Centro di GeoTecnologie CGT, 52027 San Giovanni Valdarno, Italy
3 Università degli Studi di Milano and INFN, Sezione di Milano, 20133 Milano, Italy
4 Helmholtz–Zentrum Dresden–Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany
5 Università di Genova and INFN Sezione di Genova, Genova, 16146 Genova, Italy
6 Institute of Nuclear Research (ATOMKI), 4026 Debrecen, Hungary
7 INFN, Laboratori Nazionali del Gran Sasso (LNGS), 67010 Assergi ( AQ), Italy
8 Dipartimento di Fisica Sperimentale, Università di Torino and INFN Sezione di Torino, 10125 Torino, Italy
9 Dipartimento di Scienze Fisiche, Università di Napoli Federico II, and INFN Sezione di Napoli, 80126 Napoli, Italy
10 Dipartimento di Fisica, Università degli studi di Perugia and INFN, Sezione di Perugia, 06123 Perugia, Italy
11 Institut für Experimentalphysik, Ruhr–Universität Bochum, 44780 Bochum, Germany
12 INAF – Osservatorio Astronomico di Collurania, 64100 Teramo, Italy
13 Seconda Università di Napoli, 81100 Caserta; and INFN Sezione di Napoli, 80126 Napoli, Italy
14 CNR IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l’Ingegneria e per i Materiali, Università di Brescia, Brescia, Italy
Accepted: 22 July 2011
Context. The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T ≃ 30 × 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the red giant branch (RGB) phase of the star or to the pollution of the primordial gas by an early population of massive asymptotic giant branch (AGB) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion.
Aims. The activation of this cycle depends on the rate of the 15N(p, γ)16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances.
Methods. We present a new measurement of the 15N(p, γ)16O reaction performed at LUNA covering for the first time the center of mass energy range 70−370 keV, which corresponds to stellar temperatures between 65 × 106 K and 780 × 106 K. This range includes the 15N(p, γ)16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars.
Results. With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.
Key words: stars: AGB and post-AGB / nuclear reactions, nucleosynthesis, abundances / novae / cataclysmic variables
Present address: Inst. of Experimental Physics University of Warsaw ul. Hoza 69 00–682 Warszawa, Poland.
Present address: Nuclear Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd MS 88–R0192, Berkeley, CA 94720–8101, USA.
© ESO, 2011
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