Keele Research Repository

A prerequisite for probing theoretical evolutionary models for high-mass stars is the determination of stellar physical properties with a high accuracy. We do this for three binary systems containing components with masses above 10 M⊙: V478 Cyg, AH Cep, and V453 Cyg. New high-resolution and high-S/N échelle spectra were secured and analysed using spectral disentangling, yielding improved orbital elements and the individual spectra for the component stars. In conjunction with a re-analysis of archival light curves, the stellar masses and radii were measured to accuracies of 1.5–2.5 per cent and 1.0–1.9 per cent, respectively. Detailed spectroscopic analysis then yielded atmospheric parameters and abundances for C, N, O, Mg, and Si. Abundances were also determined for V578 Mon. These results allowed a detailed comparison to the predictions of stellar evolutionary models. No star in our sample fits its position on the evolutionary track for its dynamical mass, leaving mass discrepancy (or alternatively overluminosity) an open problem in theoretical modelling. Moreover, the CNO abundances cluster around the initial values with mean values log (N/C) = −0.56 ± 0.06 and log (N/O) = −1.01 ± 0.06. No trend in the CNO abundances for single OB stars are found for the eight high-mass stars analysed here, as well in an extended sample including literature results. This opens an important question on the role of binarity in terms of tides on damping internal mixing in stars residing in binary systems.