Cyclic variability of the accretion disk in the eclipsing binary OGLE-LMC-DPV-065

Abstract

Context. The long photometric cycle observed in Algol OGLE-LMC-DPV-065 (OGLE05200407-6936391), and other similar systems, still challenges explanation. It is currently thought that a variable mass transfer rate could modify the structure of the accretion disk surrounding the more massive star, producing modulations of the global system brightness.Aims. We revisited I-band Optical Gravitational Lensing Experiment (OGLE) photometric time series spanning 20 years, with the aim of detecting and analyzing possible changes in the accretion disk properties, namely, radial and vertical extension and also temperature, and explored the existence of shock regions.Methods. We solved the inverse problem yielding the best configuration of stellar and disk parameters for explaining the variability of the light curve on the orbital as well as the long-cycle timescales. A simple model allowed us to estimate the relative mass transfer rate, and the disk parameters were analyzed to evaluate their dependence and variability.Results. We find that changes in the accretion disk properties reproduce the light curve variability patterns observed on the orbital and long-term cycle timescales. The mass transfer rate is highest and the disk thickness minimum at the maximum of the long-term cycle. The large vertical thicknesses suggest motions at scales beyond the classic scale height dominating the disk vertical structure while the disk almost always remains within the tidal radius.Conclusions. We conclude that the long-term cycle can be explained by a variable disk and that the mass transfer rate plays a fundamental role in establishing these changes.