FURTHER CRITICAL TESTS OF STELLAR EVOLUTION BY MEANS OF DOUBLE-LINED ECLIPSING BINARIES

The most accurately measured stellar masses and radii come from detach ed, double-lined eclipsing binaries, as compiled by Andersen. We prese nt a detailed quantitative comparison of these fundamental data with e volution models for single stars computed with our evolution code, bot h with and without the effects of enhanced mixing or overshooting beyo nd the convective cores. We use the same prescription for overshooting that Schroder, Pols & Eggleton found to reproduce the properties of z eta Aurigae binaries. For about 80 per cent of the 49 binary systems i n the sample, both sets of models provide a good fit to both stars at a single age and metallicity within the observational uncertainties. W e discuss possible causes for the discrepancies in the other systems. For only one system, Al Hya, do the enhanced-mixing models provide a s ignificantly better fit to the data. For two others (WX Cep and TZ For ) the fit to the enhanced-mixing models is also better. None of the ot her systems can individually distinguish between the models with and w ithout enhanced mixing. However, the number of systems in a post-main- sequence phase is in much better agreement with the enhanced-mixing mo dels. This test provides supportive evidence for extended mixing in ma in-sequence stars in the range 2-3 M-..