2005A&A...436L..39S

We have imaged ε Indi B, the closest brown dwarf binary known, with VISIR at the VLT in three narrow-band mid-infrared bandpasses located around 8.6µm, 10.5µm and 11.3µm. We are able to spatially resolve both components, and determine accurate mid-infrared photometry for both components independently. In particular, our VISIR observations probe the NH₃ feature in the atmospheres of the cooler and warmer brown dwarfs. For the first time, we can disentangle the contributions of the two components, and find that ε IndiBb is in good agreement with recent ``cloud-free'' atmosphere models having an effective temperature of T_eff=800K. With an assumed age of 1Gyr for the ε Indi system, component Ba agrees more with T_eff≃1100K rather than with T_eff=1200K, as suggested by SPITZER spectroscopic observations of the combined ε Indi B system (Roellig et al., 2004ApJS..154..418R). Even higher effective temperatures appear inconsistent with our absolute photometry, as they would imply an unphysical small size of the brown dwarf ε Indi Ba.