Discoveries of very massive planets, on one hand, and very low mass isolated brown dwarfs, on the other hand, show that the brown dwarf and the planetary mass ranges widely overlap. When these low mass brown dwarfs are close and bright enough to be observed in spectroscopy, their atmospheres are much easier to study than similar exoplanets that lie nearby their very bright host stars. When we identified CFBDSIR214947.2-040308.9 (Delorme et al 2012), it appeared as a good candidate member of the AB-Doradus young moving group and together with the low gravity features in its spectrum made it a unique T type isolated planetary-mass object. In order to ascertain its nature and determine its physical properties, we conducted additional observations: X-Shooter spectroscopy from 0.8 to 2.3 μm, mid-IR photometry with the Spitzer Space Telescope, as well as a parallax follow-up over 2 years. While the spectral information confirm the low gravity or high metallicity of the atmosphere, the new kinematics safely rule out membership to any known young moving group. Therefore this object is a peculiar late T dwarf, perhaps a young free floating planet or an older, heavier brown dwarf with supersolar metallicity.

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Poster #240