Determination of the astrophysical S factor for C-11(p,gamma)N-12 from the N-12 -> C-11+p asymptotic normalization coefficient

Abstract

The evolution of very low-metallicity, massive stars depends critically on the amount of CNO nuclei that they produce. Alternative paths from the slow 3alpha process to produce CNO seed nuclei could change their fate. The C-11(p,gamma)N-12 reaction is an important branch point in one such alternative path. At energies appropriate to stellar evolution of very low-metallicity, massive stars, nonresonant capture dominates the reaction rate. We have determined the astrophysical S factor for the C-11(p,gamma)N-12 reaction using the asymptotic normalization coefficient for N-12-->C-11+p to fix the nonresonant capture rate. In our experiment, a 110 MeV C-11 radioactive beam was used to study the(14)N(C-11,N-12)C-13 peripheral transfer reaction and the asymptotic normalization coefficient, (C-peff(12N))(2)=(C-p1/2(12N))(2)+(C-p3/2(12N))(2)=1.73+/-0.25 fm(-1), was extracted from the measured cross section. The contributions from the second resonance and interference effects were estimated using an R-matrix approach with the measured asymptotic normalization coefficient and the latest value for Gamma(gamma). We find the S factor for C-11(p,gamma)N-12 is significantly larger than previous estimates. As a result, the required density for it to contribute is reduced, and more CNO material may be produced.