Measurement of the reactions $^{17}$O$(\alpha, \gamma)^{21}$Ne and $^{17}$O$(\alpha,$ n)$^{20}$Ne and their impact on the weak s process

The ratio of the reaction rates of the competing channels $^{17}$O$(\alpha, \gamma)^{21}$Ne and $^{17}$O$(\alpha,$ n)$^{20}$Ne determines the efficiency of $^{16}$O as a neutron poison in the weak s process in low metallicity 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 $\gamma$ channel is of negligible strength. We present results of the first measurement of the reaction $^{17}$O$(\alpha, \gamma)^{21}$Ne and an improved study of the reaction $^{17}$O$(\alpha,$ n)$^{20}$Ne, including an independent measurement of the $^{17}$O$(\alpha,$ n$_1$)$^{20}$Ne channel, enabling a simultaneous R-Matrix fit to both the n$_0$ and the n$_1$ channels. The new data were used as input for stellar network calculations and their impact on the weak s process is discussed.