2MASS J09393548-2448279: THE COLDEST AND LEAST LUMINOUS BROWN DWARF BINARY KNOWN?

Determinations of the luminosity and atmospheric properties of the T8 brown dwarf 2MASS J09393548 - 2448279 are presented, based on Spitzer IRAC and IRS observations and ground-based astrometry. We find log(10) (L-bol/L-circle dot) = -5.69 +/- 0.03 for this source, comparable to the current low-luminosity record holder 2MASS J04151954 - 0935066. However, modeling of near- and mid-infrared spectral data indicates an effective temperature of 600 +/- 35 K, roughly 100 K cooler than 2M0415. These parameters require a highly inflated radius for 2M0939 (R approximate to 0.13 R-circle dot) which cannot be reconciled with brown dwarf structure models. However, if this source is an unresolved, equal-mass binary, then the reduced luminosity of each component (L-bol approximate to 10(-6) L-circle dot) can be brought into agreement with the inferred atmospheric parameters for an age of 0.4-12 Gyr and component masses of 0.01-0.05 M-circle dot. This hypothesis can be tested through future high-resolution imaging and/or spectroscopic observations.