17O(α,γ)21Neand 17O(α,n)20Nefor the weak s process

The ratio of the reaction rates of the competing channels 17 O (αγ) 21 Ne and 17 O (α,n) 20 Ne determines the efficiency of 16 O as a neutron poison in the s process in low metallicity rotating stars. It has a large impact on the element production, either producing elements to the mass range of A=90 in case of a significant poisoning effect or extending the mass range up to the region of A=150 if the γ channel is of negligible strength. We present an improved study of the reaction 17 O (α,n) 20 Ne , including an independent measurement of the 17 O (α,n 1 ) 20 Ne channel. A simultaneous R-Matrix fit to both the n0 and the n1 channels has been performed. New reaction rates, including recent data on the 17 O (α,γ) 21 Ne reaction, have been calculated and used as input for stellar network calculations and their impact on the s process in rotating massive stars is discussed.