Dwarfs Cooler Than M: The Definition of Spectral Type L Using Discoveries form the 2-Micron All-Sky Survey (2MASS)

Because the TiO and VO bands, which dominate the far-optical portions of late-M spectra, disappear in these cooler dwarfs, we define a new spectral class L in wich metallic oxides are replaced by metallic hydrides and neutral alkali metals as the major spectroscopic signatures.