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A prerequisite for probing theortical evolutionary models for high-mass starsis the determination of stellar physical properties with a high accuracy. We dothis for three binary systems containing components with masses above 10 Msun:V478 Cyg, AH Cep and V453 Cyg. New high-resolution and high-S/N echelle spectrawere secured and analysed using spectral disentangling, yielding improvedorbital elements and the individual spectra for the component stars. Inconjuction with a re-analysis of archival light curves, the stellar masses andradii were measured to accuracies of 1.5-2.5% and 1.0-1.9%, respectively.Detailed spectroscopic analysis then yielded atmospheric parameters andabundances for C, N, O, Mg and Si. Abundances were also deter- mined for V578Mon. These results allowed a detailed comparison to the predictions of stellarevolutionary models. No star in our sample fits its position on theevolutionary track for its dynamical mass, leaving mass discrepancy (oralternatively overluminosity) an open problem in theoretical modelling.Moreover, the CNO abundances cluster around the initial values with mean valueslog(N/C) = -0.56 +/- 0.06 and log(N/O) = -1.01 +/- 0.06. No trend in the CNOabundances for single OB stars are found for the eight high-mass stars analysedhere, as well in an extended sample including literature results. This opens animportant question on the role of binarity in terms of tides on dampinginternal mixing in stars residing in binary systems.

monthly notices of the royal astronomical society

Physical properties and CNO abundances for high-mass stars in four  main-sequence detached eclipsing binaries: V478 Cyg, AH Cep, V453 Cyg and  V578 Mon