2001ApJ...561L.119N

We have obtained near-infrared spectra of three L dwarfs discovered by the Two Micron All Sky Survey, 1506+13 (L3), 1507-16 (L5), and 0920+35 (L6.5). From the comparison of the H- and K-band spectra of these L dwarfs, we have found the presence of methane absorption in 0920+35. This implies that detectable methane absorption in the H and K bands, usually considered the signature of a T dwarf, can be present in objects classified optically as late L. Methane detection in L dwarfs is consistent with the presence of a dust layer deep in the atmosphere, as the unified model of Tsuji suggests.