A sample of 542 eclipsing binaries ( EBs ) with periods shorter than 2 d were selected from the Microlensing Observations in Astrophysics ( MOA ) EB catalogue \citep 2017MNRAS.470..539L for eclipse-time variation analysis .
For this sample we were able to obtain the time series from MOA-II that span 9.5 yr. We discovered 91 EBs , out of the 542 EBs , with detected light-travel-time effect signals suggesting the presence of tertiary companions of orbiting periods from 250 d -28 yr .
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 with periods shorter than 0.3 d. If only the contact binaries of periods < 0.26 d are considered , the frequency even goes to the unit .
Our results suggest that contact binaries with periods close to the 0.22-d contact binary limit are commonly accompanied by relatively close tertiary companions .