  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 NH3 and CO
in terms of the surface gravity of Gl 229B, which remains poorly constrained.
The metallicity increases with increasing gravity and is below the solar value
unless Gl 229B is a high-gravity brown dwarf with log g(cgs) ~ 5.5. The NH3
abundance is determined from both the H and 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.

Astrophysics