Rapid apsidal motion in eccentric eclipsing binaries: OX Cassiopeia, PV Cassiopeia, and CO Lacertae

¹ Astronomical Institute, Faculty of Mathematics and Physics, Charles University Prague, V Holešovičkách 2, 182 00 Praha 8, Czech Republic e-mail: Petr.Svaricek@seznam.cz; wolf@cesnet.cz
² Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18 080 Granada, Spain e-mail: claret@iaa.es
³ Astronomical Institute, Academy of Sciences, 251 65 Ondřejov, Czech Republic e-mail: lenka@asu.cas.cz
⁴ Private Observatory, Velká Úpa 193, 542 21 Pec pod Sněžkou, Czech Republic e-mail: brat@snezkou.cz
⁵ Public Observatory, Vsetínská 78, 575 01 Valašské Meziříčí, Czech Republic e-mail: lsmelcer@astrovm.cz
⁶ Institute of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic

Received: 6 June 2007
Accepted: 16 October 2007

Abstract

Aims.Double-lined eclipsing binaries are a traditional tool to test the capability of the stellar evolutionary models. If such binaries show apsidal motion, it is also possible to check, in addition to their absolute dimensions, some aspects of their internal structure. In order to perform this additional test, we monitored the times of a minimum of three eclipsing binaries with accurate absolute dimensions.

Methods.Approximately thirty new precise times of minimum light recorded with CCD photometers were obtained for three early-type eccentric-orbit eclipsing binaries OX Cas (P = , e = 0.041), PV Cas (, 0.032), and CO Lac (, 0.029).  diagrams were analyzed by the Lacy's method using all reliable timings found in the literature, and the elements of apsidal motion were improved. On the other hand, stellar models computed for the precise observed masses of the three systems were used as theoretical tools to compare with the observed shift in the periastron position.

Results.We confirm very short periods of apsidal motion of approximately 38.2, 91.0, and 43.4 years for OX Cas, PV Cas, and CO Lac, respectively. The relativistic effects are negligible, being up to 6% of the total apsidal motion rate in all systems. The corresponding observed apsidal motion rates are in good agreement with the theoretical predictions, except for the case of PV Cas, whose components seem to be more mass concentrated than the models predict.