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CFBDSIR 2149-0403: young isolated planetary-mass object or high-metallicity low-mass brown dwarf?

Abstract : Aims. We conducted a multi-wavelength, multi-instrument observational characterisation of the candidate free-floating planet CFBDSIR J214947.2−040308.9, a late T-dwarf with possible low-gravity features, in order to constrain its physical properties.Methods. We analysed nine hours of X-shooter spectroscopy with signal detectable from 0.8 to 2.3 μm, as well as additional photometry in the mid-infrared using the Spitzer Space Telescope. Combined with a VLT/HAWK-I astrometric parallax, this enabled a full characterisation of the absolute flux from the visible to 5 μm, encompassing more than 90% of the expected energy emitted by such a cool late T-type object. Our analysis of the spectrum also provided the radial velocity and therefore the determination of its full 3D kinematics.Results. While our new spectrum confirms the low gravity and/or high metallicity of CFBDSIR 2149, the parallax and kinematics safely rule out membership to any known young moving group, including AB Doradus. We use the equivalent width of the K i doublet at 1.25 μm as a promising tool to discriminate the effects of low-gravity from the effects of high-metallicity on the emission spectra of cool atmospheres. In the case of CFBDSIR 2149, the observed K i doublet clearly favours the low-gravity solution. Conclusions. CFBDSIR 2149 is therefore a peculiar late-T dwarf that is probably a young, planetary-mass object (2–13 MJup, <500 Myr) possibly similar to the exoplanet 51 Eri b, or perhaps a 2–40 MJup brown dwarf with super-solar metallicity.
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Submitted on : Saturday, October 31, 2020 - 6:37:34 PM
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P. Delorme, T. Dupuy, J. Gagné, C. Reylé, T. Forveille, et al.. CFBDSIR 2149-0403: young isolated planetary-mass object or high-metallicity low-mass brown dwarf?. Astronomy and Astrophysics - A&A, EDP Sciences, 2017, 602, pp.A82. ⟨10.1051/0004-6361/201629633⟩. ⟨hal-01716449⟩

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