Eclipse timing variation analysis of OGLE-IV eclipsing binaries towards the Galactic Bulge – I. Hierarchical triple system candidates

We report a study of the eclipse timing variation (ETV) of short period (P1 ≤ 6d) eclipsing binaries (EBs) monitored during the photometric survey optical gravitational lensing experiment-IV. From the 425 193 EBs, we selected approximately 80 000 binaries that we found suitable for further examination. Among them, we identified 992 potential hierarchical triple (or multiple) system candidates exhibiting light-travel time effect (LTTE). Besides, we obtained the orbital parameters of these systems and carried out statistical analyses on the properties of these candidates. We found that (i) there is a significant lack of triple systems where the outer period is less than 500 d, (ii) the distribution of the outer eccentricities has a maximum around e2 ≈ 0.3, and (iii) the outer mass ratio calculated from an estimated minimum mass of the third component is lower than q2 ∼ 0.5 for the majority of the sample. We also present some systems that deserve special attention: (i) There are four candidates that show double periodic ETV, which we explain by the presence of a fourth companion; (ii) For two systems, the perturbations of the third component are also found to be significant therefore we give a combined dynamical and LTTE ETV solution; and (iii) For one system, the third component is found to be probably in the substellar mass domain.