  We present parallaxes of 11 mid-to-late T dwarfs observed in the UKIRT
Infrared Deep Sky Survey. We use these results to test the reliability of model
predictions in magnitude-color space, determine a magnitude-spectral type
calibration, and, estimate a bolometric luminosity and effective temperature
range for the targets. We used observations from the UKIRT WFCAM instrument
pipeline processed at the Cambridge Astronomical Survey Unit. The parallaxes
and proper motions of the sample were calculated using standard procedures. The
bolometric luminosity was estimated using near- and mid-infrared observations
with two different methods. The corresponding effective temperature ranges were
found adopting a large age-radius range. We show the models are unable to
predict the colors of the latest T dwarfs indicating the incompleteness of
model opacities for NH3, CH4 and H2 as the temperature declines. We report the
effective temperature ranges obtained.
