Enhancement of Double-Close-Binary Quadruples

Abstract

Double-close-binary quadruples (2+2 systems) are hierarchical systems of four stars where two shortperiod 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 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±2.6 times higher than what is expected from random pairings of field stars. At most a factor of ∼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 ∼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.