The 0.8 to 14.5 mu m Spectral Energy Distributions of Mid-L to Mid-T Dwarfs

We fit theoretical model atmospheres to the spectral energy distribution of 21 L and T dwarfs recently observed with the Spitzer Space Telescope to identify and isolate four key physical parameters used in the model characterization of their atmospheres. The wide range of wavelengths observed (similar to 0.6 to 14.5 mu m) lets us constrain almost independently the four model parameters used to describe these photospheres: effective temperature (T-eff), grain sedimentation (f(sed)), vertical gas transport efficiency (K-zz), and gravity. We find that the ratio of the mid-infrared to near-infrared flux is a good indicator of T-eff, while the slope in the near-infrared is strongly dependent on f(sed). The CH4 hands found at 2, 3 and h mu m are sensitive to the timescale for vertical mixing. and gravity will influence the flux at 2 mu m.