Long photometric cycle and disk evolution in the β Lyrae-type binary OGLE-BLG-ECL-157529

Context. The subtype of hot algol semidetached binaries dubbed double periodic variables (DPVs) are characterized by a photometric cycle longer than the orbital one, whose nature has been related to a magnetic dynamo in the donor component controlling the mass transfer rate. Aims. We aim to understand the morphologic changes observed in the light curve of OGLE-BLG-ECL-157529 that are linked to the long cycle. In particular, we want to explain the changes in the relative depth of primary and secondary eclipses. Methods. We analyzed I and V-band OGLE photometric times series spanning 18.5 years and modeled the orbital light curve. Results. We find that OGLE-BLG-ECL-157529 is a new eclipsing Galactic DPV of orbital period 24d​​.8, and that its long cycle length decreases in amplitude and length during the time baseline. We show that the changes in the orbital light curve can be reproduced considering an accretion disk of variable thickness and radius that surrounds the hottest stellar component. Our models indicate changes in the temperatures of the hot spot and the bright spot during the long cycle, and also in the position of the bright spot. This, along with the changes in disk radius, might indicate a variable mass transfer in this system.