Clouds and Chemistry: Brown Dwarf Atmospheric Properties from Optical and Infrared Colors

The optical and infrared colors of L and T dwarfs are sensitive to cloud sedimentation and chemical processes in their atmospheres. In particular the J − K color of a cooling brown dwarf is sensitive to the vertical distribution of condensates in its atmosphere. Only atmosphere models which include sedimentation of condensates are able to reproduce the observed trends in J −K in which objects first become redder, then bluer with falling effective temperature. The Sloan Digital Sky Survey color i − z is sensitive to assumptions surrounding the alkali metal chemistry. Chemical equilibrium models which account for cloud sedimentation predict redder colors, by up to 2 magnitudes, than models which neglect sedimentation. The i − z vs. J − K color-color diagram is thus interesting for the window it opens into diverse atmospheric processes. In addition, we predict the locus in this color-color diagram of brown dwarfs cooler than yet found.