October 2008 • 2008ApJ...685.1183L
Abstract • We present Keck laser guide star observations of two T2.5 dwarfs—2MASS J11061197+2754225 and 2MASS J14044941-3159329—using NIRC2 on Keck II and find 2MASS J14044941-3159329 to be a 0.13'' binary. This system has a secondary that is 0.45 mag brighter than the primary in J band, but 0.49 mag fainter in H band and 1.13 mag fainter in Ks band. We use this relative photometry along with near-infrared synthetic modeling performed on the integrated light spectrum to derive component types of T 1 +/- 1 for the primary and T 5 +/- 1 for the secondary. Optical spectroscopy of this system obtained with Magellan/LDSS-3 is also presented. This is the fourth L/T transition binary to show a flux reversal in the 1-1.2 μm regime, and this one has the largest flux reversal. Unless the secondary is itself an unresolved binary, the J-band magnitude difference between the secondary and primary shows that the J-band "bump" is indeed a real feature and not an artifact caused by unresolved binarity.Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.