Infrared Colors of L and T Dwarfs
S.K. Leggett, D.A. Golimowski, X. Fan, T.R. Geballe
& G.R. Knapp
Institute: Joint Astronomy Centre Hawaii
Institute: The Johns Hopkins University
Institute: Institute for Advanced Study Princeton
Institute: Gemini Observatory Hawaii
Institute: Princeton University Observatory
Contact Email: skl@jach.hawaii.edu
Abstract:
We discuss the behaviour of the JHKL'M' colors of L and T dwarfs,
based on new photometric and spectroscopic data obtained at the
United Kingdom Infrared Telescope in Hawaii. We have measured
the first accurate M' photometry for L and T dwarfs. The K-M'
colors of T dwarfs are much bluer than predicted by published
models, suggesting that CO may be more abundant than expected,
as has been found spectroscopically for the T6 dwarf Gl229B.
We also find that K-L' increases monotonically through most of
the M, L, and T subclasses, but it is approximately constant
between types L6 and T5, due to the onset of CH_4 absorption at
the blue edge of the L' bandpass. The JHK colors of L
dwarfs show significant scatter, suggesting variations in the
amount and properties of photospheric dust, and indicating that
it may not be possible to associate a unique T_eff with a given
L spectral type. The H-K colors of the later T dwarfs also show
some scatter which we suggest is due to variations in
pressure--induced H_2 opacity, which is sensitive to gravity
(or age for a brown dwarf) and metallicity.
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Manuscript submitted: 2001-Sep-6
"The Future of Cool-Star Astrophysics", 2003, Eds. A. Brown,
G. M. Harper, & T. R. Ayres.
Proceedings of 12th Cambridge Workshop on Cool Stars, Stellar Systems,
& The Sun,
© 2003 University of Colorado.