The Close Binary Frequency of Wolf-Rayet Stars as a Function of Metallicity in M31 and M33

Here we investigate whether the inability of the Geneva evolutionary models to predict a large enough WC/WN ratio at high metallicities (while succeeding at lower metallicities) is due to their single star nature. We hypothesize that Roche-lobe overflow in close binary systems may produce a greater number of WC stars at higher metallicities. But, this would suggest that the frequency of close massive binaries is metallicity dependent. We now present our results based on observations of ~100 Wolf-Rayet binaries in the varying metallicity environments of M31 and M33.