We present the results of a search for wide binary systems among 783 members of three nearby young associations : Taurus-Auriga , Chamaeleon I , and two subgroups of Upper Scorpius .
Near-infrared ( JHK ) imagery from 2MASS was analyzed to search for wide ( 1-30″ ; \sim 150-4500 AU ) companions to known association members , using color-magnitude cuts to reject likely background stars .
We identify a total of 131 candidate binary companions with colors consistent with physical association , of which 39 have not been identified previously in the literature .
Our results suggest that the wide binary frequency is a function of both mass and environment , with significantly higher frequencies among high-mass stars than lower-mass stars and in the T associations than in the OB association .
We discuss the implications for wide binary formation and conclude that the environmental dependence is not a direct result of stellar density or total association mass , but instead might depend on another environmental parameter like the gas temperature .
We also analyze the mass ratio distribution as a function of mass and find that it agrees with the distribution for field stars to within the statistical uncertainties .
The binary populations in these associations generally follow the empirical mass-maximum separation relation observed for field binaries , but we have found one candidate low-mass system ( USco-160611.9-193532 ; M _ { tot } \sim 0.4 M _ { \sun } ) which has a projected separation ( 10.8″ ; 1550 AU ) much larger than the suggested limit for its mass .
Finally , we find that the binary frequency in the USco-B subgroup is significantly higher than in the USco-A subgroup and is consistent with the measured values in Taurus and Cham I .
This discrepancy , the absence of high-mass stars in USco-B , and its marginally distinct kinematics suggest that it might not be directly associated with the OB associations of Sco-Cen , but instead represents an older analogue of the younger \rho Oph or Lupus associations .