The Role of Mass and Environment in Multiple‐Star Formation: A 2MASS Survey of Wide Multiplicity in Three Young Associations

We present the results of a search for wide binary systems among 783 membersof three nearby young associations: Taurus-Auriga, Chamaeleon I, and twosubgroups of Upper Scorpius. Near-infrared (JHK) imagery from 2MASS wasanalyzed to search for wide (1-30"; ~150-4500 AU) companions to knownassociation members, using color-magnitude cuts to reject likely backgroundstars. We identify a total of 131 candidate binary companions with colorsconsistent with physical association, of which 39 have not been identifiedpreviously in the literature. Our results suggest that the wide binaryfrequency is a function of both mass and environment, with significantly higherfrequencies among high-mass stars than lower-mass stars and in the Tassociations than in the OB association. We discuss the implications for widebinary formation and conclude that the environmental dependence is not a directresult of stellar density or total association mass, but instead might dependon another environmental parameter like the gas temperature. We also analyzethe mass ratio distribution as a function of mass and find that it agrees withthe distribution for field stars to within the statistical uncertainties. Thebinary populations in these associations generally follow the empiricalmass-maximum separation relation observed for field binaries, but we have foundone candidate low-mass system (USco-160611.9-193532; Mtot~0.4 Msun) which has aprojected separation (10.8"; 1550 AU) much larger than the suggested limit forits mass. (Abridged)