Volume 631, November 2019
|Number of page(s)||18|
|Section||Planets and planetary systems|
|Published online||01 November 2019|
Orbital and spectral analysis of the benchmark brown dwarf HD 4747B ★
Observatoire astronomique de l’Université de Genève,
51 Ch. des Maillettes,
2 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
3 Max Planck Institute for Astronomy, Koenigstuhl 17 69117 Heidelberg, Germany
4 Laboratoire d’Astrophysique de Marseille, 38, rue Frédéric Joliot-Curie 13388 Marseille cedex 13, France
5 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC University of Paris 06, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
6 Department of Physics, University of Oxford, Oxford, UK
7 Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
8 Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
9 Center for Space and Habitability, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
10 Université Cote d’Azur, OCA, CNRS, Lagrange, France
11 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
12 INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
13 Centre de Recherche Astrophysique de Lyon, CNRS, Université Lyon 1, 9 avenue Charles André, 69561 Saint Genis-Laval-Cedex, France
14 The University of Michigan, Ann Arbor, MI 48109, USA
15 NOVA Optical Infrared Instrumentation Group, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
16 European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
17 Núcleo de Astonomía, Facultad de Ingeniería, Universidad Diego Portales, A. Ejercito 441, Santiago, Chile
18 Escuela de Ingeniería Industrial, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
Accepted: 13 May 2018
Context. The study of high-contrast imaged brown dwarfs and exoplanets depends strongly on evolutionary models. To estimate the mass of a directly imaged substellar object, its extracted photometry or spectrum is used and adjusted with model spectra together with the estimated age of the system. These models still need to be properly tested and constrained. HD 4747B is a brown dwarf close to the H burning mass limit, orbiting a nearby (d = 19.25 ± 0.58 pc), solar-type star (G9V); it has been observed with the radial velocity method for over almost two decades. Its companion was also recently detected by direct imaging, allowing a complete study of this particular object.
Aims. We aim to fully characterize HD 4747B by combining a well-constrained dynamical mass and a study of its observed spectral features in order to test evolutionary models for substellar objects and to characterize its atmosphere.
Methods. We combined the radial velocity measurements of High Resolution Echelle Spectrometer (HIRES) and CORALIE taken over two decades and high-contrast imaging of several epochs from NACO, NIRC2, and SPHERE to obtain a dynamical mass. From the SPHERE data we obtained a low-resolution spectrum of the companion from Y to H band, and two narrow band-width photometric measurements in the K band. A study of the primary star also allowed us to constrain the age of the system and its distance.
Results. Thanks to the new SPHERE epoch and NACO archival data combined with previous imaging data and high-precision radial velocity measurements, we were able to derive a well-constrained orbit. The high eccentricity (e = 0.7362 ± 0.0025) of HD 4747B is confirmed, and the inclination and the semi-major axis are derived (i = 47.3 ± 1.6°, a = 10.01 ± 0.21 au). We derive a dynamical mass of mB = 70.0 ± 1.6 MJup, which is higher than a previous study but in better agreement with the models. By comparing the object with known brown dwarfs spectra, we derive a spectral type of L9 and an effective temperature of 1350 ± 50 K. With a retrieval analysis we constrain the oxygen and carbon abundances and compare them with the values from the HR 8799 planets.
Key words: binaries: general / binaries: spectroscopic / binaries: visual / brown dwarfs / planets and satellites: atmospheres / techniques: high angular resolution
© ESO 2019
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