Enhancement of double-close-binary quadruples

Double-close-binary quadruples (2 + 2 systems) are hierarchical systems of four stars where two short-period binary systems move around their common centre 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 d and with outer separations of greater than or similar to 1000 au. All of these systems but one are newly discovered by this work, and we catalogue 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 similar to 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 similar to 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.

Automated summary

Using Gaia data, we discovered eight new double-close-binary quadruple systems, suggesting an enhancement in the formation of short-period binaries due to the presence of wide companions.