K dwarf triples and quadruples in the SUPERWIDE catalog of 90,000 nearby wide binaries

The SUPERWIDE catalog is an all-sky catalog of ∼90,000 wide binaries with projected orbital separations ∼100 to 100,000 AU, mostly located within 500 pc of the Sun. These consist of common proper motion (CPM) pairs of high proper motion stars (> 40 mas/yr). A Bayesian analysis using positions, proper motions and distances from Gaia Data Release 2 (DR2) shows these pairs to have probabilities > 99% of being gravitationally bound systems. Here, we examine K+K wide binaries, which allow for easy identification of unresolved higher-order systems because the K dwarf main sequence is narrow and unresolved subsystems are easily identified as over-luminous. We found 980 systems where at least one of the wide components is over-luminous, which means they are higher-order systems (triples and quadruples). Although metallicity efffects generally complicate the identification of over-luminous stars, we show that this can be easily accounted for in wide binaries, making the identification of unresolved subsystems relatively straightforward. Taking these effects into account, we calculate the higher-order multiplicity fraction to be 39.6%.