A study of the light travel time effect in short-period MOA eclipsing binaries via eclipse timing

A sample of 542 eclipsing binaries (EBs) with periods shorter than 2 days were selected from the MOA EB catalogue for eclipse time variation analysis. For this sample we were able to obtain the time series from MOA-II that span 9.5 years. We discovered 91 EBs, among these 542 EBs, with detected light-travel-time effect signals suggesting the presence of tertiary companions of orbiting periods from 250 days to 28 years. The frequency of EBs with tertiary companions in our sample increases as the period decreases and reaches a value of 0.65 for contact binaries of periods shorter than 0.3 days. If only the contact binaries of periods < 0.26 days are considered, the frequency even goes to the unit. Our results suggest that contact binaries with periods close to the 0.22-day contact binary limit are commonly accompanied by relatively close tertiary companions. Furthermore, excess at extremely high eccentricity was noticed for our 91 triple candidates.