Characterizing Young Brown Dwarfs Using Low‐Resolution Near‐Infrared Spectra

We present near-infrared (1.0-2.4 micron) spectra confirming the youth and cool effective temperatures of 6 brown dwarfs and low mass stars with circumstellar disks toward the Chamaeleon II and Ophiuchus star forming regions. The spectrum of one of our objects indicates that it has a spectral type of ~L1, making it one of the latest spectral type young brown dwarfs identified to date. Comparing spectra of young brown dwarfs, field dwarfs, and giant stars, we define a 1.49-1.56 micron H2O index capable of determining spectral type to within 1 sub-type, independent of gravity. We have also defined an index based on the 1.14 micron sodium feature that is sensitive to gravity, but only weakly dependent on spectral type for field dwarfs. Our 1.14 micron Na index can be used to distinguish young cluster members (t