The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low‐Resolution Near‐Infrared Spectra

We present the first results of a near-infrared (0.96-2.31 micron)spectroscopic survey of M, L, and T dwarfs obtained with NIRSPEC on the Keck IItelescope. Our new survey has a resolving power of R = 2000 and is comprised oftwo major data sets: 53 J-band (1.14-1.36 micron) spectra covering all spectraltypes from M6 to T8 with at least two members in each spectral subclass(wherever possible), and 25 flux-calibrated spectra from 1.14 to 2.31 micronsfor most spectral classes between M6 and T8. Sixteen of these 25 objects haveadditional spectral coverage from 0.96-1.14 microns to provide overlap withoptical spectra. Spectral flux ratio indexes for prominent molecular bands arederived and equivalent widths (EWs) for several atomic lines are measured. Wefind that a combination of four H2O and two CH4 band strengths can be used forspectral classification. Weak (EW~1-2 angstrom) atomic lines of Al I and Ca Idisappear at the boundary between M and L types.