Discovery of a T Dwarf Binary with the Largest Known J-Band Flux Reversal

Abstract

We present Keck laser guide star observations of two T2.5 dwarfs - 2MASS J11061197+2754225 & 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 mags brighter than the primary in J-band but 0.49 mags fainter in H-band and 1.13 mags 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 T1 for the primary and T5 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 micron 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.

13 pages, 8 figures; accepted to ApJ - added two extra paragraphs explaining our methodology in more detail, updated reference list

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