New Young Brown Dwarfs in the Orion Molecular Cloud 2/3 Region

Forty new low mass members with spectral types ranging from M4−M9 have been confirmed in the Orion Molecular Cloud 2/3 region. Through deep, I−, z−, J−, H− and K−band photometry of a 20 × 20 field in OMC 2/3, we selected brown dwarf candidates for follow-up spectroscopy. Low resolution farred and near-infrared spectra were obtained for the candidates, and 19 young brown dwarfs in the OMC 2/3 region are confirmed. They exhibit spectral types of M6.5−M9, corresponding to approximate masses of 0.075−0.015 M⊙ using the evolutionary models of Baraffe et al. (1998). At least one of these bona fide young brown dwarfs has strong Hα emission, indicating that it is actively accreting. In addition, we confirm 21 new low mass members with spectral types of M4−M6, corresponding to approximate masses of 0.35−0.10 M⊙ in OMC 2/3. By comparing pre-main sequence tracks to the positions of the members in the H-R diagram, we find that most of the brown dwarfs are less than 1 Myr, but find a number of low mass stars with inferred ages greater than 3 Myr. The discrepancy in the stellar and substellar ages is due to our selection of only low luminosity sources; however, the presence of such objects implies the presence of an age spread in the OMC 2/3 region. We discuss possible reasons for this apparent age spread. Subject headings: infrared: stars – open clusters and associations: individual (Orion Molecular Clouds 2 and 3, OMC 2/3) – stars: formation – stars: imaging – stars: low-mass, brown dwarfs – techniques: spectroscopic