Structural and compositional properties of brown dwarf disks: the case of 2MASS J04442713+2512164

In order to improve our understanding of substellar formation, we have performed a compositional and structural study of a brown dwarf disk. We present the result of photometric, spectroscopic and imaging observations of 2MASS J04442713+2512164, a young brown dwarf (M7.25) member of the Taurus association. Our dataset, combined with results from the literature, provides a complete coverage of the spectral energy distribution from the optical to the millimeter including the first photometric measurement of a brown dwarf disk at 3.7mm, and allows us to perform a detailed analysis of the disk properties. The target was known to have a disk. High resolution optical spectroscopy shows that it is intensely accreting, and powers a jet and an outflow. The disk structure is similar to that observed for more massive TTauri stars. Spectral decomposition models of Spitzer/IRS spectra suggest that the mid-infrared emission from the optically thin disk layers is dominated by grains with intermediate sizes (1.5micron). Crystalline silicates are significantly more abondant in the outer part and/or deeper layers of the disk, implying very efficient mixing and/or additional annealing processes. Sub-millimeter and millimeter data indicate that most of the disk mass is in large grains (>1mm)