67 Additional L Dwarfs Discovered by the Two Micron All Sky Survey

By J. D. Kirkpatrick, I. Neill Reid, J. Liebert, J. Gizis, A. Burgasser, D. Monet, C. Dahn, B. Nelson, Rik J. Williams. 2000

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We present JHKs photometry, far red spectra, and spectral classifications for an additional 67 L dwarfs discovered by the Two Micron All Sky Survey. One of the goals of this new search was to locate more examples of the latest L dwarfs. Of the 67 new discoveries, 17 have types of L6 or later. Analysis of these new discoveries shows that Hα emission has yet to be convincingly detected in any L dwarf later than type L4.5, indicating a decline or absence of chromospheric activity in the latest L dwarfs. Further analysis shows that 16 (and possibly four more) of the new L dwarfs are lithium brown dwarfs and that the average line strength for those L dwarfs showing lithium increases until type ∼L6.5 V, then declines for later types. This disappearance may be the first sign of depletion of atomic lithium as it begins to form into lithium-bearing molecules. Another goal of the search was to locate nearer, brighter L dwarfs of all subtypes. Using absolute magnitudes for 17 L dwarf systems with trigonometric parallax measurements, we develop spectrophotometric relations to estimate distances to the other L dwarfs. Of the 67 new discoveries, 21 have photometric distances placing them within 25 pc of the Sun. A table of all known L and T dwarfs believed to lie within 25 pc—53 in total — is also presented. Using the distance measurement of the coolest L dwarf known, we calculate that the gap in temperature between L8 and the warmest known T dwarfs is less than 350 K and probably much less. If the transition region between the two classes spans a very small temperature interval, this would explain why no transition objects have yet been uncovered. This evidence, combined with model fits to low-resolution spectra of late M and early L dwarfs, indicates that L-class objects span the range 1300 K ≲ Teff ≲ 2000 K. The near-infrared color-color diagram shows that L dwarfs fall along a natural, redder extension of the well-known M dwarf track. These near-infrared colors get progressively redder for later spectral types, with the L dwarf sequence abruptly ending near (J-H, H-Ks, J-Ks) ≈ (1.3, 0.8, 2.1).

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

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Citations in the corpus

The UKIRT Infrared Deep Sky Survey ZY JHK photometric system: passbands and synthetic colours (2006, unknown): “…(2000a), Geballe et al. (1996), Geballe et al. (2001), Geballe et al (2002), Kirkpatrick, Beichman & Skrutskie (1997), Kirkpatrick et al. (1999b), Kirkpatrick et al. (2000), Knapp et al. (2004), Leggett et al. (2000; 2001; 2002a; 2002b), Liebert et al. (2000), McLean et al. (2003), Reid et al.…”
A Unified Near-Infrared Spectral Classification Scheme for T Dwarfs (2005, background): “…earlier-type T dwarfs is weak, with Teff roughly constant from L8 to T5 despite significant changes in near infrared spectral energy distributions (Kirkpatrick et al. 2000; Burgasser et al. 2002c; Dahn et al. 2002; Tinney, Burgasser, & Kirkpatrick 2003; Golimowski et al. 2004; Nakajima et al.…”
Ultradeep Near-Infrared ISAAC Observations of the Hubble Deep Field South: Observations, Reduction, Multicolor Catalog, and Photometric Redshifts (2002, background): “However, measurements by Kirkpatrick et al. (2000) show the L dwarf sequence abruptly stopping at (Js Ks)J 2.1 (the subscript noting Johnson magnitudes; see x 3.1 for the transformations to the AB system), whereas even cooler T dwarfs have much bluer (Js Ks)J 0 colors than expected from their…”
A Search for L Dwarf Binary Systems (2000, background): “The I-band absolute magnitude is ∼ 0.9 magnitudes fainter than the L8 dwarf 2M1632 (Table 1), while the estimated J-band absolute magnitude, MJ ∼ 15.2, is 0.2 magnitudes fainter than faintest L dwarf currently known, Gl 584C (K00), and only 0.3 magnitudes brighter than the value measured for Gl 229B”
Calculations of the Far-Wing Line Profiles of Sodium and Potassium in the Atmospheres of Substellar-Mass Objects (2002, background): “…(Na), potassium (K), cesium (Cs), rubidium (Rb), and lithium (Li) are prevalent in the spectra of L dwarfs, T dwarfs, and irradiated giant planets (Kirkpatrick et al. 1999, 2000; Burgasser et al. 1999, 2000, 2002; Burrows,Marley, & Sharp 2000, hereafter BMS00; Burrows et al. 2001, 2002; Liebert…”
MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, unknown): “These objects are 2MASS 0825196+211552 (Kirkpatrick et al. 2000), SDSS 085758+570851 (Geballe et al. 2002), and SDSS J151643.”
New spectral types L and T (2005, methodology): “Nonetheless, a set of optical spectra of 92 field L dwarfs was taken at the 10 m Keck Observatory and were analyzed by Kirkpatrick et al. (2000).”
COLORS AND KINEMATICS OF L DWARFS FROM THE SLOAN DIGITAL SKY SURVEY (2010, background): “…and the SDSS/2MASS colors for the rest of the dwarfs are similar to those in previous work (H02; Knapp et al. 2004; Chiu et al. 2006), but the J −KS colors calculated from the photometric sample are consistently bluer than those found in previous work (Kirkpatrick et al. 2000; Faherty et al. 2009).”
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, background): “…(13) Gagné et al. (2014a); (14) Gagné et al. (2015a); (15) Gizis (2002); (16) Gizis et al. (2012); (17) Hall (2002a); (18) Jameson et al. (2008); (19) Kirkpatrick et al. (2000); (20) Kirkpatrick et al. (2001); (21) Kirkpatrick et al. (2008); (22) Kirkpatrick et al. (2010); (23) Kirkpatrick et…”
The Brown Dwarf Desert at 75-1200 AU (2004, background): “While recent searches have detected numerous brown dwarfs in the field (e.g., Kirkpatrick et al. 2000) and in clusters (e.g., Moraux et al. 2003), very few companions to stars have been found with masses in the substellar range between 12 and 75 MJ. 3 Brown dwarf companions can be detected either…”
Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program (2004, methodology): “L dwarfs from these surveys have been identified by many authors (Delfosse et al. 1997; Kirkpatrick et al. 1999; Kirkpatrick et al. 2000; 1www.sdss.org 2www.ipac.caltech.edu/2mass 3cdsweb.u-strasbg.fr/denis.html Fan et al. 2000; Hawley et al. 2002; Geballe et al. 2002; Schneider et al. 2002), as…”
Characterization of M, L, and T Dwarfs in the Sloan Digital Sky Survey (2002, background): “These discoveries culminated in the definition of the L spectral class (Kirkpatrick et al. 1999, hereafter K99; Martin et al. 1999; Kirkpatrick et al. 2000, hereafter K00; Basri et al. 2000).”
The Spectra of T Dwarfs. II. Red Optical Data (2003, background): “A general weakening of the Li i line is observed in substellar late-type L dwarfs (Kirkpatrick et al. 2000), and the absence of this line in the T dwarfs is consistent with a temperature effect.”
Multiplicity of Nearby Free-floating Ultracool Dwarfs: A Hubble Space Telescope WFPC2 Search for Companions (2003, methodology): “Kirkpatrick et al. (2000) evaluated its distance at 29 pc, considering a single object.”
THE BROWN DWARF KINEMATICS PROJECT I. PROPER MOTIONS AND TANGENTIAL VELOCITIES FOR A LARGE SAMPLE OF LATE-TYPE M, L, AND T DWARFS (2008, methodology): “Defining the (J −Ks)avg for spectral bins has been done in previous ultracool dwarf studies such as Kirkpatrick et al. (2000), Vrba et al. (2004), and West et al. (2008) but we have included all ultracool dwarfs in the dwarfarchives complilation and the updated photometry reported in Chiu et al.…”
Seventy-One New L and T Dwarfs from the Sloan Digital Sky Survey (2006, background): “…many known L and T dwarfs have yielded well-defined classi- fication schemes and valuable information about the chemical compositions, temperatures, and other physical characteristics of ultracool dwarfs (Kirkpatrick et al. 2000; Burgasser et al. 2002b, 2006a; G02; K04; Golimowski et al. 2004a).”
Infrared Spectra and Spectral Energy Distributions of Late M and L Dwarfs (2000, methodology): “The spectral types in Table 1 are based on optical spectra and are taken from Kirkpatrick, Henry, & Simmons (1995) ; Kirkpatrick et al. (1997b, 1999b, 2000) ; and Fan et al. (2000).”