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Title:
67 Additional L Dwarfs Discovered by the Two Micron All Sky Survey
Authors:
Kirkpatrick, J. Davy; Reid, I. Neill; Liebert, James; Gizis, John E.; Burgasser, Adam J.; Monet, David G.; Dahn, Conard C.; Nelson, Brant; Williams, Rik J.
Affiliation:
AA(Infrared Processing and Analysis Center, Mail Stop 100-22, California Institute of Technology, Pasadena, CA 91125; , ), AB(Department of Physics and Astronomy, University of Pennsylvania, 209 South 33d Street, Philadelphia, PA 19104-6396 ), AC(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 ), AD(Infrared Processing and Analysis Center, Mail Stop 100-22, California Institute of Technology, Pasadena, CA 91125; , ), AE(Department of Physics, Mail Stop 103-33, California Institute of Technology, Pasadena, CA 91125;), AF(US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002; , ), AG(US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002; , ), AH(Infrared Processing and Analysis Center, Mail Stop 100-22, California Institute of Technology, Pasadena, CA 91125; , ), AI(Department of Astronomy, MSC 152, California Institute of Technology, Pasadena, CA 91126-0152)
Publication:
The Astronomical Journal, Volume 120, Issue 1, pp. 447-472. (AJ Homepage)
Publication Date:
07/2000
Origin:
UCP
AJ Keywords:
Infrared Radiation, Stars: Atmospheres, Stars: Distances, Stars: Fundamental Parameters, Stars: Low-Mass, Brown Dwarfs
DOI:
10.1086/301427
Bibliographic Code:
2000AJ....120..447K

Abstract

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). Portions of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation.
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