Enhancement of Double-Close-Binary Quadruples

TL;DR

This paper reports the discovery of eight new double-close-binary quadruple star systems using Gaia data, revealing a higher-than-expected occurrence rate and suggesting a formation mechanism influenced by wide companions.

Contribution

It introduces eight newly identified 2+2 quadruple systems with short inner periods, and provides evidence for an enhanced formation rate of close binaries in wide-separation pairs.

Findings

Eight new 2+2 quadruple systems discovered

Occurrence rate of quadruples is 7.3 times higher than random expectation

Enhanced formation of short-period binaries linked to wide companions

Abstract

Double-close-binary quadruples (2+2 systems) are hierarchical systems of four stars where two short-period binary systems move around their common center of mass on a wider orbit. Using Gaia Early Data Release 3, we search for comoving pairs where both components are eclipsing binaries. We present eight 2+2 quadruple systems with inner orbital periods of $<$ 0.4 days and with outer separations of $\gtrsim 1000$ AU. All but one system are newly discovered by this work, and we catalog their orbital information measured from their light curves. We find that the occurrence rate of 2+2 quadruples is 7.3 $\pm$ 2.6 times higher than what is expected from random pairings of field stars. At most a factor of $\sim$2 enhancement may be explained by the age and metallicity dependence of the eclipsing binary fraction in the field stellar population. The remaining factor of $\sim$3 represents a genuine enhancement of the production of short-period binaries in wide-separation ($>10^3$ AU) pairs, suggesting a close binary formation channel that may be enhanced by the presence of wide companions.