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

• Published in: The Astrophysical journal Vol. 685; no. 1; pp. 313 - 332
• Main Authors: Peterson, Dawn E, Megeath, S. T, Luhman, K. L, Pipher, J. L, Stauffer, J. R, Barrado y Navascués, D, Wilson, J. C, Skrutskie, M. F, Nelson, M. J, Smith, J. D
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 20.09.2008; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Molecular clouds; open clusters and associations: individual (Orion Molecular Clouds 2 and 3, OMC 2/3); infrared: stars; Open clusters; Star clusters; stars: formation; stars: imaging; Star formation; Low-mass stars; Brown dwarf stars; techniques: spectroscopic; Infrared star; stars: low-mass, brown dwarfs
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/590527

Forty new low-mass members with spectral types ranging from M4 to M9 have been confirmed in the Orion Molecular Cloud (OMC) 2/3 region. Through deep, I-, z super([image] )-, J-, H-, and K-band photometry of a [image] field in OMC 2/3, we selected brown dwarf candidates for follow-up spectroscopy. Low-resolution far-red 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 [image] using the evolutionary models of Baraffe et al. At least one of these bona fide young brown dwarfs has strong H alpha 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 [image] 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.