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Published August 1, 2007 | Published
Journal Article Open

USco J1606-1935: An Unusually Wide Low-Mass Triple System?


We present photometric, astrometric, and spectroscopic observations of USco J160611.9-193532 AB, a candidate ultrawide (~1600 AU), low-mass (M_(tot) ~ 0.4 M_⊙) multiple system in the nearby OB association Upper Scorpius. We conclude that both components are young, comoving members of the association; we also present high-resolution observations that show that the primary is itself a close binary system. If the Aab and B components are gravitationally bound, the system would fall into the small class of young multiple systems that have unusually wide separations as compared to field systems of similar mass. However, we demonstrate that physical association cannot be assumed purely on probabilistic grounds for any individual candidate system in this separation range. Analysis of the association's two-point correlation function shows that there is a significant probability (25%) that at least one pair of low-mass association members will be separated in projection by ≾ 15", so analysis of the wide binary population in Upper Sco will require a systematic search for all wide systems; the detection of another such pair would represent an excess at the 98% confidence level.

Additional Information

© 2007 The American Astronomical Society. Received 2007 March 5; accepted 2007 April 2. The authors thank C. Slesnick for providing guidance in the analysis of young stellar spectra, P. Cameron for sharing his NIRC2 astrometric calibration results prior to publication, and the anonymous referee for returning a helpful and very prompt review. The authors also wish to thank the observatory staff, and particularly the Keck LGSAO team, for their tireless efforts in commissioning this valuable addition to the observatory. Finally, we recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work makes use of data products from the Two Micron All-Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/ California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This work also makes use of data products from the DENIS project, which has been partly funded by the SCIENCE and the HCM plans of the European Commission under grants CT920791 and CT940627. It is supported by INSU, MEN, and CNRS in France, by the State of Baden-Wu¨rttemberg in Germany, by DGICYT in Spain, by CNR in Italy, by FFwFBWF in Austria, by FAPESP in Brazil, by OTKA grants F-4239 and F-013990 in Hungary, and by the ESO C&EE grant A-04-046. Finally, our research has made use of the USNOFS Image and Catalogue Archive operated by the United States Naval Observatory, Flagstaff Station (http://www.nofs.navy.mil/data/fchpix).

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