Evolution of young brown dwarf disks in the mid-infrared

Abstract

We have imaged two bona-fide brown dwarfs with TReCS/GEMINI-S and find mid-infrared excess emission that can be explained by optically thick dust disk models. In the case of the young (≈2 Myr) Cha Hal we measure fluxes at 10.4 μm and 12.3 μm that are fully consistent with a standard flared disk model and prominent silicate emission. For the μ10 Myr old brown dwarf 2MASS1207-3932 located in the TW Hydrae association we find excess emission at 8.7 μm and 10.4 μm with respect to the photosphere, and confirm disk accretion as a likely cause of its strong activity. Disks around brown dwarfs likely last at least as long as their low-mass stellar counterparts in the T-Tauri phase. Grain growth, dust settling, and evolution of the geometry of brown dwarf disks may appear on a timescale of 10 Myr and can be witnessed by observations in the mid-infrared.