Broad levels in $^{17}$O and their relevance for the astrophysical s-process

Abstract

Levels in $^{17}$O affect the astrophysical s-process in two opposite ways. The neutron production is enhanced by resonances in the $^{13}$C($\alpha$,$n$)$^{16}$O reaction at excitation energies around 7 MeV in $^{17}$O, and the number of available neutrons is reduced by low-lying resonances in the $^{16}$O($n$,$\gamma$)$^{17}$O reaction corresponding to levels in $^{17}$O with excitation energies of $4-5$ MeV. The present work uses the $^{19}$F($d$,$\alpha$)$^{17}$O reaction to determine absolute widths of the relevant levels in $^{17}$O. The results improve the uncertainties of the previously adopted values and resolve a discrepancy between recent studies for the $1/2^+$ level close to the threshold of the $^{13}$C($\alpha$,$n$)$^{16}$O reaction. In addition, improved excitation energies and widths are provided for several states in $^{17}$O up to excitation energies close to 8 MeV.