Apsidal motion and absolute parameters for five LMC eccentric eclipsing binaries^⋆,⋆⋆

Astronomical Institute, Charles University in Prague, Faculty of Mathematics and Physics, 180 00 Praha 8, V Holešovičkách 2, Czech Republic
e-mail: zasche@sirrah.troja.mff.cuni.cz

Received: 11 June 2013
Accepted: 15 July 2013

Abstract

Aims. As part of our observational projects at the La Silla Danish 1.54-meter telescope, we aim to measure the precise times of minimum light for eccentric eclipsing binaries in the Large Magellanic Cloud, needed for accurate determination of apsidal motion. Many new times of minima were derived from the photometric databases OGLE and MACHO. Several new minima were also observed. Five early-type and eccentric-orbit eclipsing binaries: HV 982 (P = 5.^d34, e = 0.15), HV 2274 (5.^d73, 0.17), MACHO 78.6097.13 (3.^d11, 0.05), MACHO 81.8881.47 (3.^d88, 0.22), and MACHO 79.5377.76 (2.^d64, 0.06) were studied.

Methods. The O–C diagrams of the systems were analysed using all reliable timings found in the literature, and new or improved elements of apsidal motion were obtained. Light and radial velocity curves of MACHO 81.8881.47 and MACHO 79.5377.76 were analysed using the program PHOEBE.

Results. We derived for the first time or significantly improved the relatively short periods of apsidal motion of 211 (12), 127 (8), 48 (13), 103 (20), and 42 (19) years, respectively. The internal structure constants, log k₂, were found to be –2.37, –2.47, –2.17, –2.02, and –1.86 respectively, under the assumption that the component stars rotate pseudosynchronously. The relativistic effects are weak, up to 6% of the total apsidal motion rate. The masses for MACHO 81.8881.47 resulted in 5.51 (0.21) and 5.40 (0.19) M_⊙, while for MACHO 79.5377.76 the masses are 11.26 (0.35) and 11.27 (0.35) M_⊙, respectively.