Microscopic study of the 14O(α,p)17F reactions at stellar energies

We have studied the 14O(α,p)17F reaction at astrophysically important energies within a microscopic multichannel calculation based on the framework of the generator coordinate method. Our study gives a consistent description of the 18Ne states close to the α-threshold as well as of the direct (α,p) reaction process which has not been considered in previous calculations. We find that the 14O(α,p)17F rate at temperatures T ≤ 5x108 K is strongly influenced by the 2+ resonance at E = 30 keV above the α-threshold and by the direct reaction cross section. At higher temperatures 18Ne states not present in our model space become important. We have estimated the influence of these resonances on the 14O(α,p)17F rate within the standard formalism developed by Fowler assigning experimentally unknown spins to the states on the basis of a Thomas-Ehrman shift analysis using theoretical and experimental informations on the respective analogue states in 18O. We find an 14O(α,p)17F rate which is noticeably higher than the rate estimated by Wiescher et al. for T ≤ 5x108 K. Both rates are of the same magnitude for T ≥ 109 K. Our estimate predicts that the 14O(α,p)17F rate is compatible to the 15O(α,γ)19Ne rate under nova conditions. For explosive burning on accreting neutron stars our rate allows for a break-out from the CNO cycle via the 14O(α,p)17F reaction. (orig.)