New RR Lyrae variables in binary systems

TL;DR

This study searches for binary RR Lyrae stars using OGLE data, identifying 12 firm candidates and estimating that over 4% of RR Lyrae stars are in binary systems, enhancing understanding of their binary fraction.

Contribution

The paper introduces a method using $O-C$ diagrams to detect binary RR Lyrae stars and reports the discovery of 12 firm binary candidates in the Galactic bulge.

Findings

Identified 12 firm binary RR Lyrae candidates.

Estimated that over 4% of RR Lyrae stars are in binary systems.

Extended baseline analysis up to 17 years with OGLE data.

Abstract

Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated ($O-C$) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 years, leading to a final sample of 12 firm binary candidates. We provide $O-C$ diagrams and binary parameters for this final sample, and also discuss the properties of 8 additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that $\gtrsim 4$ per cent of the RRL reside in binary systems.