Abstract
We present new high-resolution infrared spectra of the T dwarf Gliese
229B in the J, H, and K bandpasses. We analyze each of these as well
as previously published spectra to determine its metallicity and
the abundances of NH, and CO in terms of the surface gravity of G1
229B, which remains poorly constrained. The metallicity increases
with increasing gravity and is below the solar value unless G1 229B
is a high-gravity brown dwarf with log g (cgs) approximate to 5.5.
The NH3 abundance is determined from both the Hand the K-band spectra,
which probe two different levels in the atmosphere. We find that
the abundance from the K-band data is well below that expected from
chemical equilibrium, which we interpret as strong evidence for dynamical
transport of NH3 in the atmosphere. This is consistent with the previous
detection of CO and provides additional constraints on the dynamics
of the atmosphere of this T dwarf.
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