A Statistical Survey of Peculiar L and T Dwarfs in SDSS, 2MASS, and WISE

Abstract

We present the final results from a targeted search for brown dwarfs with unusual near-infrared colors. From a positional cross-match of SDSS, 2MASS and WISE, we have identified 144 candidate peculiar L and T dwarfs. Spectroscopy confirms that 20 of the objects are peculiar or are candidate binaries. Nine of the 420 objects in our sample are young ($\lesssim$200 Myr; 2.1%) and another 8 (1.9%) are unusually red with no signatures of youth. With a spectroscopic $J-K_s$ color of 2.58 $\pm$ 0.11 mag, one of the new objects, the L6 dwarf 2MASS J03530419+0418193, is among the reddest field dwarfs currently known and is one of the reddest objects with no signatures of youth known to date. We have also discovered another potentially very low gravity object, the L1 dwarf 2MASS J00133470+1109403, and independently identified the young L7 dwarf 2MASS J00440332+0228112, first reported by Schneider and collaborators. Our results confirm that signatures of low gravity are no longer discernible in low to moderate resolution spectra of objects older than $\sim$200 Myr. The 1.9% of unusually red L dwarfs that do not show other signatures of youth could be slightly older, up to $\sim$400 Myr. In this case a red $J-K_s$ color may be more diagnostic of moderate youth than individual spectral features. However, its is also possible that these objects are relatively metal-rich, and so have an enhanced atmospheric dust content.

27 pages, 7 figures, 5 tables, accepted to AJ

References in corpus (11)

• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839-0446358
• Discovery of Two Nearby, Peculiar L Dwarfs from the 2MASS Proper Motion Survey: Young or Metal-Rich?
• SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of Fourteen Candidate Binaries with Late-M/Early-L and T Dwarf Components
• Near-infrared cross-dispersed spectroscopy of brown dwarf candidates in the Upper Sco association
• An Infrared High Proper Motion Survey Using 2MASS and SDSS: Discovery of M, L and T Dwarfs
• Discovery of a High Proper Motion L Dwarf Binary: 2MASS J15200224-4422419AB
• Exploring the Role of Sub-micron Sized Dust Grains in the Atmospheres of Red L0 - L6 Dwarfs