Evidence for a High Altitude Haze on Brown Dwarf

Brown dwarfs are celestial objects with masses between those of large planets and small stars, that emit primarily infrared radiation. Unlike main sequence stars, brown dwarfs cannot reach high enough temperatures to conduct nuclear fusion within their cores. As a result, brown dwarfs have surface temperatures below 2200 K, at which point silicate clouds can form in their atmospheres. We present overlapping Hubble Space Telescope (HST; Wide Field Camera 3) and Spitzer Space Telescope observations of a variable brown dwarf with patchy silicate clouds in its atmosphere. The brown dwarf varies in brightness as it rotates, with an amplitude of ~5% from 1.1-1.7 microns (HST), and ~2.5% at 3.6-microns (Spitzer). Using a Mie-scattering model we determined that a lognormal distribution of sub-micron size grains at a high altitude in the atmosphere can approximately reproduce the observed variations at all wavelengths.