A sample of 542 eclipsing binaries (EBs) with periods shorter than 2 d were selected from the Microlensing Observations in Astrophysics (MOA) EB catalogue (Li et al. 2017) for eclipse-time variation analysis. For this sample we were able to obtain the time series from MOA-II that span 9.5yr. 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 < 0.26d 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.
@article{arxiv.1804.11272,
title = {A study of light travel time effect in short-period MOA eclipsing binaries via eclipse timing},
author = {M. C. A. Li and N. J. Rattenbury and I. A. Bond and T. Sumi and D. P. Bennett and N. Koshimoto and F. Abe and Y. Asakura and R. Barry and A. Bhattacharya and M. Donachie and P. Evans and A. Fukui and Y. Hirao and Y. Itow and K. Masuda and Y. Matsubara and Y. Muraki and M. Nagakane and K. Ohnishi and To. Saito and A. Sharan and D. J. Sullivan and D. Suzuki and P. J. Tristram and A. Yonehara},
journal= {arXiv preprint arXiv:1804.11272},
year = {2018}
}