Using the Infrared Array Camera ( IRAC ) aboard the Spitzer Space Telescope , we have obtained mid-infrared photometry of the least massive known brown dwarf in the Chamaeleon I star-forming region .
For this young brown dwarf , OTS 44 , we have constructed a spectral energy distribution ( SED ) from 0.8-8 µm by combining the measurements at 3.6 , 4.5 , 5.8 , and 8.0 µm from IRAC with ground-based photometry at I , J , H , and K .
The resulting SED for OTS 44 exhibits significant excess emission longward of 3 µm relative to the SED expected from the photosphere of the brown dwarf .
We have successfully modeled the source of this excess emission in terms of an irradiated viscous accretion disk with \dot { M } \lesssim 10 ^ { -10 } M _ { \odot } yr ^ { -1 } .
With a spectral type of M9.5 and a mass of \sim 15 M _ { Jup } , OTS 44 is now the coolest and least massive brown dwarf observed to have a circumstellar disk .
These measurements demonstrate that disks exist around brown dwarfs even down to the deuterium burning mass limit and the approximate upper mass limit of extrasolar planetary companions .