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Sixty-seven Additional L Dwarfs Discovered by the Two Micron All Sky Survey (2MASS) | | J. Davy Kirkpatrick
; I. Neill Reid
; James Liebert
; John E. Gizis
; Adam J. Burgasser
; David G. Monet
; Conard C. Dahn
; Brant Nelson
; Rik J. Williams
; | | Date: |
22 Mar 2000 | | Subject: | astro-ph | | 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 H-alpha 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 4 more) of the new L dwarfs are lithium brown dwarfs and that the average line strength for those L dwarfs showing lithium increases until roughly 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 parsecs of the Sun. A table of all known L and T dwarfs believed to lie within 25 parsecs - 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 350K 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 dwarfs span the range 1300K < Teff < 2000K. | | Source: | arXiv, astro-ph/0003317 | | Services: | Forum | Review | PDF | Favorites | |
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