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(Abridged) Eclipsing, spectroscopic double-lined binary star systems (SB2)are excellent laboratories for calibrating theories of stellar interiorstructure and evolution. We aim to investigate the mass discrepancy in binarystars. We study the effect of near-core mixing on the mass of the convectivecore of the stars and interpret the results in the context of the massdiscrepancy. Two scenarios are considered, where individual stellar componentsof a binary system are treated independent of each other and where they areforced to have the same age and initial chemical composition. We find that themass discrepancy is present in our sample and that it is anti-correlated withthe surface gravity of the star. No correlations are found with otherfundamental and atmospheric parameters, including the stellar mass. The massdiscrepancy can be partially accounted for by increasing the amount ofnear-core mixing in stellar evolution models. We also find that ignoring themicroturbulent velocity and turbulent pressure in stellar atmosphere models ofhot evolved stars results in overestimation of their effective temperature byup to 8%. Together with enhanced near-core mixing, this can almost entirelyaccount for the 30% mass discrepancy found for the evolved primary component ofV380 Cyg. We find a strong link between the mass discrepancy and the convectivecore mass. The mass discrepancy can be solved by considering the combinedeffect of extra near-core boundary mixing and consistent treatment in thespectrum analysis of hot evolved stars. Our binary modelling results inconvective core masses between 17 and 35% of the stellar mass, in excellentagreement with results from gravity-mode asteroseismology of single stars. Thisimplies larger helium core masses near the end of the main sequence thananticipated so far.

The mass discrepancy in intermediate- and high-mass eclipsing binaries: the need for higher convective core masses