CFBDSIR 2149-0403: young isolated planetary-mass object or high-metallicity low-mass brown dwarf?⋆
1 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
2 The University of Texas at Austin, Department of Astronomy, 2515 Speedway, Stop C1400, Austin, Texas 78712-1205, USA
3 Carnegie Institution of Washington DTM, 5241 Broad Branch Road NW, Washington, DC 20015, USA
4 Institut UTINAM, CNRS UMR 6213, Observatoire des Sciences de l’Univers THETA Franche-Comté Bourgogne, Univ. Bourgogne Franche-Comté, 41bis avenue de l’Observatoire, 25000 Besançon, France
5 IfA, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
6 Institut de Recherche sur les Exoplanètes, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
7 Univ. Lyon, ENS de Lyon, Univ. Lyon1, CNRS, Centre de Recherche Astrophysique de Lyon UMR 5574, 69007 Lyon Cedex 07, France
8 Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
9 Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI96743, USA
10 UC Santa Cruz, ISB 159/1156 High St, Santa Cruz, CA 95060, USA
Received: 1 September 2016
Accepted: 1 March 2017
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.
Key words: brown dwarfs / planets and satellites: gaseous planets / stars: atmospheres / methods: observational / techniques: spectroscopic
Based on observations obtained with X-shooter on VLT-UT2 at ESO-Paranal (run 091.D-0723). Based on observations obtained with HAWKI on VLT-UT4 (run 089.C-0952, 090.C-0483, 091.C-0543,092.C-0548,293.C-5019(A) and run 086.C-0655(A)). Based on observations obtained with ISAAC on VLT-UT3 at ESO-Paranal (run 290.C-5083). Based on observation obtained with WIRCam at CFHT (program 2012BF12). Based on Spitzer Space telescope DDT observation (program 10166).
© ESO, 2017