Observational approach to the chemical evolution of high-mass binaries

The complexity of composite spectra of close binaries makes the study of the individual stellar spectra extremely difficult. For this reason there exists very little information on the chemical composition of high-mass stars in close binaries, despite its importance for understanding the evolution of massive stars and close binary systems. A way around this problem exists: spectral disentangling allows a time-series of composite spectra to be decomposed into their individual components whilst preserving the total signal-to-noise ratio in the input spectra. Here we present the results of our ongoing project to obtain the atmospheric parameters of high-mass components in binary and multiple systems using spectral disentangling. So far, we have performed detailed abundance studies for 14 stars in eight eclipsing binary systems. Of these, V380 Cyg, V621 Per and V453 Cyg are the most informative as their primary components are evolved either close to or beyond the TAMS. Contrary to theoretical predictions of rotating single-star evolutionary models, both of these stars show no abundance changes relative to unevolved main sequence stars of the same mass. It is obvious that other effects are important in the chemical evolution of components in binary stars. Analyses are ongoing for further systems, including AH Cep, CW Cep and V478 Cyg.