Exploring Contact Binaries: Photometric Analysis of Short-period Contact Binaries in OGLE SMC Field

Abstract We present a comprehensive photometric analysis of 15 short-period contact binary systems using photometric data from Optical Gravitational Lensing Experiment, All-Sky Automated Survey for Supernovae, and space-based Transiting Exoplanet Survey Satellite (TESS) observations. The light curves are modeled with the PHysics Of Eclipsing BinariEs package, and system parameter distributions are explored using a Markov Chain Monte Carlo approach. Light-curve asymmetries indicative of the O’Connell effect are detected in several systems and are successfully reproduced through the inclusion of a stellar spot in models. Flux contamination in the TESS data is accounted for by incorporating a third-light contribution. The majority of the systems exhibit inclinations ≥70° and small temperature differences between the components, consistent with efficient thermal contact. Long-term orbital period variations are investigated through O − C diagram analysis, revealing secular period changes in 15 systems. In addition to quadratic variations, cyclic modulations are identified in seven systems, which are best explained by the light-travel time effect due to tertiary companions. Secular period changes are interpreted primarily in terms of mass transfer between the components. Absolute physical parameters are derived using semimajor axes estimated from an empirical period–semimajor axis relation, providing a homogeneous scale for the sample. All systems have total masses below 1.5 M ⊙ , and most are classified as shallow-contact binaries with low fill-out factors. The contact nature of the systems is independently confirmed using the total mass-orbital angular momentum diagram. Evolutionary analysis based on mass–radius, mass–luminosity, and temperature–luminosity relations places the systems at the low-mass end of the contact binary population, consistent with their short orbital periods.