Observational tests and predictive stellar evolution

We compare 18 binary systems with precisely determined radii and masses fro m 23 to 1.1 M-. and stellar evolution models produced with our newly revise d code TYCHO. "Overshooting" and rotational mixing were suppressed in order to establish a baseline for isolating these and other hydrodynamic effects . Acceptable coeval fits are found for 16 pairs without optimizing for heav y-element or helium abundance. The precision of these tests is limited by t he accuracies of the observed effective temperatures. High-dispersion spect ra and detailed atmospheric modeling should give more accurate effective te mperatures and heavy-element abundances. PV Cas, a peculiar early A system, EK Cep B, a known post-T Tauri star, and RS Cha, a member of a young OB as sociation, are matched by pre-main-sequence models. Predicted mass loss agr ees with upper limits from IUE for CW Cep A and B. Relatively poor fits are obtained for binaries having at least one component in the mass range 1.7 < M/M-. < 2.6, whose evolution is sensitive to mixing. These discrepancies are robust and consistent with additional mixing in real stars. The predict ed apsidal motion implies that massive star models are systematically less centrally condensed than the real stars. If these effects are due to oversh ooting, then the overshooting parameter alpha (OV) increases with stellar m ass. The apsidal motion constants are controlled by radiative opacity under conditions close to those directly measured in laser experiments, making t his test more stringent than possible before.