This article has an erratum: [erratum]
Volume 627, July 2019
|Number of page(s)||13|
|Section||Letters to the Editor|
|Published online||15 July 2019|
Letter to the Editor
Constraining the properties of HD 206893 B
A combination of radial velocity, direct imaging, and astrometry data⋆
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
2 European Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla, 19001 Santiago, Chile
3 Pixyl S.A., La Tronche, France
4 GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
5 Department of Astrophysics, University of Oxford, UK
6 Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
7 Centre for Exoplanet Science, University of Edinburgh, Edinburgh, UK
8 Department of Physics, University of Oxford, UK
9 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, France
10 Observatoire de Genève, University of Geneva, 51 Chemin des Maillettes, 1290 Versoix, Switzerland
11 Space Telescope Science Institute, Baltimore, USA
12 Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
13 INAF – Osservatorio Astronomico di Padova, Italy
14 INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
15 Astronomical Observatory of Padova/Asiago, Italy
16 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
17 Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
18 Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
19 Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
20 Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
21 Escuela de Ingeniería Industrial, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
Accepted: 24 May 2019
Context. High contrast imaging enables the determination of orbital parameters for substellar companions (planets, brown dwarfs) from the observed relative astrometry and the estimation of model and age-dependent masses from their observed magnitudes or spectra. Combining astrometric positions with radial velocity gives direct constraints on the orbit and on the dynamical masses of companions. A brown dwarf was discovered with the VLT/SPHERE instrument at the Very Large Telescope (VLT) in 2017, which orbits at ∼11 au around HD 206893. Its mass was estimated between 12 and 50 MJ from evolutionary models and its photometry. However, given the significant uncertainty on the age of the system and the peculiar spectrophotometric properties of the companion, this mass is not well constrained.
Aims. We aim at constraining the orbit and dynamical mass of HD 206893 B.
Methods. We combined radial velocity data obtained with HARPS spectra and astrometric data obtained with the high contrast imaging VLT/SPHERE and VLT/NaCo instruments, with a time baseline less than three years. We then combined those data with astrometry data obtained by HIPPARCOS and Gaia with a time baseline of 24 yr. We used a Markov chain Monte Carlo approach to estimate the orbital parameters and dynamical mass of the brown dwarf from those data.
Results. We infer a period between 21 and 33 yr and an inclination in the range 20−41° from pole-on from HD 206893 B relative astrometry. The RV data show a significant RV drift over 1.6 yr. We show that HD 206893 B cannot be the source of this observed RV drift as it would lead to a dynamical mass inconsistent with its photometry and spectra and with HIPPARCOS and Gaia data. An additional inner (semimajor axis in the range 1.4–2.6 au) and massive (∼15 MJ) companion is needed to explain the RV drift, which is compatible with the available astrometric data of the star, as well as with the VLT/SPHERE and VLT/NaCo nondetection.
Key words: techniques: radial velocities / techniques: high angular resolution / astrometry / brown dwarfs / binaries: close
© A. Grandjean et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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