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SDSS J080531.84+481233.0 is a peculiar L-type dwarf that exhibits unusuallyblue near-infrared and mid-infrared colors and divergent optical (L4) andnear-infrared (L9.5) spectral classifications. These peculiar spectral traitshave been variously attributed to condensate cloud effects or subsolarmetallicity. Here I present an improved near-infrared spectrum of this sourcewhich further demonstrates the presence of weak CH4 absorption at 1.6 micronbut no corresponding band at 2.2 micron. It is shown that these features can becollectively reproduced by the combined light spectrum of a binary with L4.5and T5 components, as deduced by spectral template matching. Thus, SDSSJ080531.84+481233.0 appears to be a new low-mass binary straddling the Ldwarf/T dwarf transition, an evolutionary phase for brown dwarfs that remainspoorly understood by current theoretical models. The case of SDSSJ080531.84+481233.0 further illustrates how a select range of L dwarf/T dwarfbinaries could be identified and characterized without the need for highangular resolution imaging or radial velocity monitoring, potentiallyalleviating some of the detection biases and limitations inherent to suchtechniques.

SDSS J080531.84+481233.0: An Unresolved L Dwarf/T Dwarf Binary