1995A&A...302..741C

EK Cep is a double-lined eclipsing binary system with unique characteristics. Accurate absolute dimensions are available, a good determination of the surface lithium abundance has been made, the system is known to show apsidal motion variations, and its secondary component seems to be in the pre main sequence phase. Due to all this, it appears to be a very good candidate to test predictions made on the basis of currently adopted stellar evolutionary models. We have carried out a comparison of the observed parameters of EK Cep with theoretically predicted values, and we have found that an evolutionary age for the binary system around 2x10⁷ years verifies both components on the same isochrone. Moreover, the secondary component has been confirmed as a pre main sequence star while its more massive companion is in the begining of the hydrogen-burning phase. For the same evolutionary age, we computed the theoretical internal structure constants of the component stars and thus predicted the newtonian apsidal motion rate. The relativistic contribution is expected to be quite large (around 40% of the total value) due to the small relative radii of the two stars. For the present paper, a new determination of the observational apsidal motion rate has been made with a result of 0.00101±0.00015 degrees/cycle. This is in perfect agreement with the predicted total value. On the other hand, lithium depletion was followed during the computation of the models. For the primary component we did not find significant depletion, and for the secondary we found a depletion of only 0.1 dex which is, in fact, in good agreement with observations.