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 pm 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 mum) and L' (3.8 mum) 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 similar to100 mas. The remainder are only marginally resolved at the diffraction limit of the telescope. Sz 116, AS 205, Elias 2-22, ESO Halpha 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 similar to6 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.