2 1 A ug 2 00 9 draft Suppression of the stellar enhancement factor and the reaction 85 Rb ( p , n ) 85 Sr

It is shown that a Coulomb suppression of the stellar enhancement factor occurs in many endothermic reactions at and far from stability. Contrary to common assumptions, reaction measurements for astrophysics with minimal impact of stellar enhancement should be preferably performed for those reactions instead of their reverses, despite of their negative Q value. As a demonstration, the cross section of the astrophysically relevant Rb(p,n)Sr reaction has been measured by activation between 2.16 ≤ Ec.m. ≤ 3.96 MeV and the astrophysical reaction rates at p process temperatures for (p,n) as well as (n,p) are directly inferred from the data. Additionally, our results confirm a previously derived modification of a global optical proton potential. The presented arguments are also relevant for other αand proton-induced reactions in the p, rp, and νp processes.