Low-Mass Stars and Substellar Objects in the NGC 1333 Molecular Cloud

We present the results of near-infrared imaging and low-resolution near-infrared spectroscopy of low mass objects in the NGC 1333 molecular cloud. AJHK survey of an 11.4' x 11.7' area of the northern cluster was conducted to asensitivity of K < 16 mag. Using near-infrared magnitudes and colors from thisand previously published surveys, twenty-five brown dwarf candidates wereselected toward the high extinction cloud core. Spectra in the K band wereobtained and comparisons of the depths of water vapor absorption bands in ourcandidate objects with a grid of dwarf,subgiant, and giant standards were madeto derive spectral types. These data were then used to derive effectivetemperatures and stellar luminosities which, when combined with theoreticaltracks and isochrones for pre-main sequence objects, resulted in estimates fortheir masses and ages. The models suggest a median age for the sample of < 1Myr with substellar masses for at least 9 of the candidates including the x-rayflare source ASR 24. Surface gravities have been estimated for the brown dwarfcandidates and, for a given spectral type,found to resemble more closely dwarfsthan giants. Using the near-infrared imaging data and age estimates from thespectroscopic sample, an extinction-limited sample in the northern cluster wasdefined. Consistent with recent studies of other young clusters, this sampleexhibits an accretion disk frequency of 0.75 +-0.20 and a mass spectrum slopeacross the hydrogen-burning limit of alpha < 1.6 where dN/dM ~ M^-(alpha).Comment: 22 postscript pages, 12 postscript figures, and 3 postscript tables. Accepted for publication in the Astronomical Journal (February, 2004