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

TL;DR

This study analyzes eclipse timing variations in short-period MOA eclipsing binaries over 9.5 years, revealing a high frequency of tertiary companions, especially among the shortest period contact binaries.

Contribution

It provides the first large-scale analysis of light-travel-time effects in short-period binaries, highlighting the prevalence of tertiary companions near the 0.22-day period limit.

Findings

91 binaries show light-travel-time effect signals

Frequency of tertiaries increases with decreasing period

Nearly all contact binaries with periods < 0.26d have tertiaries

Abstract

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.