Triple-Star Candidates Among the Kepler Binaries

TL;DR

This study searches the Kepler eclipsing binary data for hierarchical triple star systems using eclipse timing variations, identifying 39 candidates and estimating that at least 20% of close binaries have tertiary companions.

Contribution

It introduces an automated method for detecting triple-star candidates from eclipse timing variations in Kepler binaries and estimates the prevalence of tertiary companions.

Findings

39 triple-star candidates identified

At least 20% of close binaries have tertiary companions

Method demonstrates potential for large-scale triple star detection

Abstract

We present the results of a search through the photometric database of eclipsing Kepler binaries (Prsa et al. 2011; Slawson et al. 2011) looking for evidence of hierarchical triple star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The "calculated" eclipse times, based on a constant period model, are subtracted from those observed. The resulting O-C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the ~1/2-hour Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O-C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called "physical" delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O-C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions.