The impact of 17O + α reaction rate uncertainties on the s-process in rotating massive stars

Massive stars are crucial to galactic chemical evolution for elements heavier than iron. Their contribution at early times in the evolution of the Universe, however, is unclear due to poorly constrained nuclear reaction rates. The competing ¹⁷O(α, γ)²¹Ne and ¹⁷O(α, n)²⁰Ne reactions strongly impact weak s-process yields from rotating massive stars at low metallicities. Abundant ¹⁶O absorbs neutrons, removing flux from the s-process, and producing ¹⁷O. The ¹⁷O(α, n)²⁰Ne reaction releases neutrons, allowing continued s-process nucleosynthesis, if the ¹⁷O(α, γ)²¹Ne reaction is sufficiently weak. While published rates are available, they are based on limited indirect experimental data for the relevant temperatures and, more importantly, no uncertainties are provided. The available nuclear physics has been evaluated, and combined with data from a new study of astrophysically relevant ²¹Ne states using the ²⁰Ne(d, p)²¹Ne reaction. Constraints are placed on the ratio of the (α, n)/(α, γ) reaction rates with uncertainties on the rates provided for the first time. The new rates favour the (α, n) reaction and suggest that the weak s-process in rotating low-metallicity stars is likely to continue up to barium and, within the computed uncertainties, even to lead.