The evolutionary status of EK Cephei: rotating and standard models

Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080 Granada, Spain e-mail: claret@iaa.es

Received: 28 March 2005
Accepted: 12 September 2005

Abstract

The evolutionary status of the double-lined eclipsing binary EK Cep is reanalysed. Due to problems with the empirical determination of its effective temperatures, we have used a different approach to compare the observations with theoretical models: we have adopted the effective temperature ratio, which is a better determined parameter from light curve analysis, instead of their absolute values. Such an approach is supported observationally by the inconsistency found in the photometric distances for both components of EK Cep. By using the effective temperature ratio, masses, radii, apsidal-motion rate and lithium depletion, we have found that standard models are able to fit the physical properties of EK Cep simultaneously at the same isochrone. In the case of rotating models, we have also found acceptable solutions without the need for a very fast rotating core. On the other hand, the apsidal-motion rate of EK Cep is critically revised.