Abundance ratio 18O/17O in hot CNO nucleosynthesis

Hot CNO burning is investigated with special emphasis on the ratio of mass 18 to mass 17 nuclei. First, claculations for constant temperature, T, and density, rho, are discussed. For T8=1 and 2 and rho=100 g cm-3, the conditions which Cowan and Rose suggested should yield high (>1) values of 18O/17O, it is found that the production of mass 18 nuclei is particularly sensitive to the rates of the reactions 18F(p, α)15O and 18F(p, γ)19Ne, which are, however, not available from experiment. Using the estimates for these rates proposed by Wagoner, one obtains values of 18O/17O which are several orders of magnitude smaller than those found by Cowan and Rose, who neglected these reactions. For 4PmsT8< or =8 and 102< or =rho< or =104 g cm-3, which may be characteristic of conditions in novae, supermassive stars, and outer zones of supernovae, substantial simultaneous overproduction (relative to the solar system value) of mass 17 and mass 18 concomitant overproduction of mass 15 nuclei greatly exceeds that of both mass 17 and mass 18 nuclei. In addition, it is found that the influence of hydrodynamic freeze-out tends to decrease that hot CNO burning probably is unable to account for high (>1) ratios of 18O/17O. Finally, the need for improved rates of several reactions governing the production of mass 17 and mass 18 nuclei is emphasized