Wednesday, July 10, 2013

1307.2243 (Markus Janson et al.)

A Multiplicity Census of Intermediate-Mass Stars in Scorpius-Centaurus    [PDF]

Markus Janson, David Lafreniere, Ray Jayawardhana, Mariangela Bonavita, Julien H. Girard, Alexis Brandeker, John E. Gizis
Stellar multiplicity properties have been studied for much of the range from the lowest to the highest stellar masses, but intermediate-mass stars from F-type to late A-type have received relatively little attention. Here we report on a Gemini/NICI snapshot imaging survey of 138 such stars in the young Scorpius-Centaurus (Sco-Cen) region, for the purpose of studying multiplicity with sensitivity down to planetary masses at wide separations. In addition to two brown dwarfs and a companion straddling the hydrogen burning limit we reported previously, here we present 26 new stellar companions and determine a multiplicity fraction within 0.1"--5.0" of 21+/-4%. Depending on the adopted semi-major axis distribution, our results imply a total multiplicity in the range of ~60--80%, which further supports the known trend of a smoothly continuous increase in the multiplicity fraction as a function of primary stellar mass. A surprising feature in the sample is a distinct lack of nearly equal-mass binaries, for which we discuss possible reasons. The survey yielded no additional companions below or near the deuterium-burning limit, implying that their frequency at >200 AU separations is not quite as high as might be inferred from previous detections of such objects within the Sco-Cen region.
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