Soft dipole mode in 17Ne and the astrophysical 2p capture on 15O

Using the two-proton-halo candidate 17Ne as an example, we discuss the possibility of a soft-dipole mode in protonrich nuclei. The study is based on a three-body model considering 17Ne as an 15O core and two protons. Our calculation predicts a relatively narrow peak in the E1 strength function which exhausts a considerable part of the E1 cluster sum rule at energies only a few MeV above the 2p threshold. We also calculate the 2p capture cross section on 15O at astrophysical conditions appropriate for explosive hydrogen burning in novae and X-ray bursts. Our calculation includes consistently resonant and non-resonant contributions to the astrophysical capture rate. We find that for a broad range of temperatures (including temperatures in excess of 109 K) the rate is dominated by non-resonant contributions.