Imaging the Circumstellar Environments of Young Binaries in Southern Star-Forming Regions

A sample of 14 pre–main-sequence visual binary systems in southern star-forming regions were imaged at 2 μm with the Keck I telescope to search for tertiary companions, scattered-light disks, and compact nebulae at linear scales of 5–100 AU. Speckle holography was used to produce images with diffraction-limited resolution and high dynamic range, and photometry in four filters between J (1.25 μm) and L′ (3.8 μm) was used to provide a diagnostic of the infrared excess. Of the 14 visual binary systems studied, nine contain components that show evidence for resolved structure. Two of them (WSB 18 and B59-1) have well-resolved tertiary companions separated from the primary stars by ∼100 mas. The remainder are only marginally resolved at the diffraction limit of the telescope. Sz 116, AS 205, Elias 2-22, ESO Hα 282, and B59-2 each have one component that is marginally resolved along one axis and unresolved on the perpendicular axis, consistent with tertiaries at separations between ∼6 and 40 mas. If all these systems are hierarchical triples, then fully half the nominal binaries in the sample are triple. The primaries in Elias 2-49 and WSB 71 are marginally resolved along all position angles, suggesting the presence of dust halos. No disks were unambiguously detected in the sample.