Eclipsing Binaries in the LMC: a Wealth of Data for Astrophysical Tests

We have analysed publicly available MACHO observations of 6833 variable stars in the Large Magellanic Cloud, classified as eclipsing binaries. After finding that a significant fraction of the sample was misclassified, we redetermined periods and variability class for all stars, producing a clean sample of 3031 eclipsing binaries. We have investigated their distribution in the period-color-luminosity space, which was used, for example, to assign a foreground probability to every object and establish new period-luminosity relations to selected types of eclipsing stars. The latter was used to test the existence of red giant contact binaries. We found that the orbital period distribution of LMC binaries is extremely similar to those of the SMC and the Milky Way. To fully utilize advantages of the MACHO database, we have also determined the rate of period change for every star. As a result, there is a significant increase in the number of known LMC binaries with apsidal motion (up to about 20), which offers an excellent sample to test theories of apsidal motion. We also discovered about 50 eclipsing binaries with cyclic period changes, suggesting the presence of a third companion. If confirmed, these systems will allow testing the effects of multiplicity in stars via modelling their orbital evolution. We also investigated the hypothesis of orbital period variations induced by mass-transfer in semidetached systems by a statistical analysis of the measured rates of period change. Finally, we discovered several eclipsing binaries with pulsating components, which offers a new way of studying oscillations in massive B-type stars through combining theories of stellar oscillations and binary star astrophysics.