Variable stars in the residual light curves of OGLE-IV eclipsing binaries towards the Galactic Bulge

Abstract

Context. The Optical Gravitational Lensing Experiment (OGLE) observed around 450 000 eclipsing binaries (EBs) towards the Galactic Bulge. Decade-long photometric observations such as these provide an exceptional opportunity to thoroughly examine the targets. However, observing dense stellar fields such as the Bulge may result in blends and contamination by close objects. Aims. We searched for periodic variations in the residual light curves of EBs in OGLE-IV and created a new catalogue for the EBs that contain ‘background’ signals after the investigation of the source of the signal. Methods. From the about half a million EB systems, we selected those that contain more than 4000 data points. We fitted the EB signal with a simple model and subtracted it. To identify periodical signals in the residuals, we used a GPU-based phase dispersion minimisation python algorithm called cuvarbase and validated the found periods with Lomb-Scargle periodograms. We tested the reliability of our method with artificial light curves. Results. We identified 354 systems where short-period background variation was significant. In these cases, we determined whether it is a new variable or just the result of contamination by an already catalogued nearby one. We classified 292 newly found variables into EB, δ Scuti, or RR Lyrae categories, or their sub-classes, and collected them in a catalogue. We also discovered four new doubly eclipsing systems and one eclipsing multiple system with a δ Scuti variable, and modelled the outer orbits of the components.