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Published September 20, 2008 | Published
Journal Article Open

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


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'-, 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 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 M☉ using the evolutionary models of Baraffe et al. 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.

Additional Information

© 2008. The American Astronomical Society. Received 2006 November 21; accepted 2008 June 2; published 2008 September 20. Print publication: Issue 1 (2008 September 20). We are grateful to N. Caldwell for the Blue Channel Spectrograph observations, and to J. Rayner and B. Bus for help with SpeX observations. We also thank M. Cushing for help with Spextool, and M. Merrill for providing some SQIID calibration data and help understanding SQIID linearity. Finally, thanks go to the anonymous referee, whose useful comments have improved this paper. Support for S.T.M. was provided in part by NASA through contract 1256790 issued by JPL/Caltech. CorMASS is supported by a generous gift from the F.H. Levinson Fund of the Peninsula Community Foundation. The authors also wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research has made use of NASA's Astrophysics Data System. Facilities: ARC (CorMASS), FLWO: 1.2m(4-Shooter), IRTF (SpeX), Keck: I(LRIS), KPNO: 2.1m (SQIID), Magellan: Clay (CorMASS), MMT (Red and Blue Channel Spectrographs), VATT (CorMASS) Some of the observations presented here were obtained at the MMT Observatory, Whipple Observatory, W.M. Keck Observatory, Las Campanas Observatory, Mount Graham International Observatory, and Apache Point Observatory. The MMT Observatory is a joint facility of the Smithsonian Institution and the University of Arizona. The W.M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The W.M. Keck Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The Apache Point Observatory 3.5 m telescope is owned and operated by the Astrophysical Research Consortium. In addition, this publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

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