The apsidal-motion test of stellar structure and evolution: an update

Aims. The recent revision of a sample of 94 double-lined eclipsing binaries with accurate absolute dimensions provides a set of 18 systems with eccentric orbits that are precise enough to carry out an updated apsidal motion test of stellar structure. The availability of these new high-quality observational data, together with improved stellar models, that include the latest opacities, stellar compressibility, resonances, and rotation, has triggered the comparison presented in this paper between theoretical and observed apsidal motion rates. Methods. The applicability of the adopted stellar models to the sample of eclipsing binaries with accurate absolute dimensions and eccentric orbits was checked with two classical tests of the good agreement between the predicted and observed effective temperatures of the component stars and a fit to a common isochrone of their position in the H-R diagram. For this comparison, stellar models were computed for the observed individual masses and incorporated the most recent input physics available, including the effects of rotation and convective core overshooting. Results. The final comparison of the theoretical and observed weighted internal-structure constants k(2) shows good agreement and no systematic effects. Observational evidence does not show more massive cores than predicted by the models as has been suggested, and this result is independent of the evolutionary status.