Issue |
A&A
Volume 587, March 2016
|
|
---|---|---|
Article Number | A55 | |
Number of page(s) | 20 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/201526465 | |
Published online | 16 February 2016 |
First light of the VLT planet finder SPHERE
I. Detection and characterization of the substellar companion GJ 758 B⋆
1 Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: arthur.vigan@lam.fr
2 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
3 Université Grenoble Alpes, IPAG, 38000 Grenoble, France
4 CNRS, IPAG, 38000 Grenoble, France
5 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
6 LESIA, Observatoire de Paris, CNRS, Université Paris Diderot, Université Pierre et Marie Curie, 5 place Jules Janssen, 92190 Meudon, France
7 Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
8 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
9 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
10 Geneva Observatory, University of Geneva, Chemin des Maillettes 51, 1290 Versoix, Switzerland
11 INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
12 Dept. of Physics and Astronomy, Macquarie University, NSW 2109, Sydney, Australia
13 Monash Centre for Astrophysics, Monash University, VIC 3800, Melbourne, Australia
14 ONERA, The French Aerospace Lab BP72, 29 avenue de la Division Leclerc, 92322 Châtillon Cedex, France
15 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
16 CNRS, CFHT, 65-1238 Mamalahoa Hwy, Kamuela HI, USA
17 Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
18 Millennium Nucleus “Protoplanetary Disk”, Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
19 INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
20 University of Amsterdam Sterrenkundig Instituut “Anton Pannekoek” Science Park 904 1098 XH Amsterdam, The Netherlands
21 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
22 CRAL, UMR 5574, CNRS, Université Lyon 1, 9 avenue Charles André, 69561 Saint-Genis-Laval Cedex, France
23 Université Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, Laboratoire J.-L. Lagrange, CS 34229, 06304 Nice Cedex 4, France
24 California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA
25 NOVA Optical-Infrared Instrumentation Group at ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
Received: 4 May 2015
Accepted: 5 November 2015
GJ 758 B is a brown dwarf companion to a nearby (15.76%) solar-type, metal-rich (M / H = + 0.2 dex) main-sequence star (G9V) that was discovered with Subaru/HiCIAO in 2009. From previous studies, it has drawn attention as being the coldest (~600 K) companion ever directly imaged around a neighboring star. We present new high-contrast data obtained during the commissioning of the SPHERE instrument at the Very Large Telescope (VLT). The data was obtained in Y-, J-, H-, and Ks-bands with the dual-band imaging (DBI) mode of IRDIS, thus providing a broad coverage of the full near-infrared (near-IR) range at higher contrast and better spectral sampling than previously reported. In this new set of high-quality data, we report the re-detection of the companion, as well as the first detection of a new candidate closer-in to the star. We use the new eight photometric points for an extended comparison of GJ 758 B with empirical objects and four families of atmospheric models. From comparison to empirical object, we estimate a T8 spectral type, but none of the comparison objects can accurately represent the observed near-IR fluxes of GJ 758 B. From comparison to atmospheric models, we attribute a Teff = 600 ± 100 K, but we find that no atmospheric model can adequately fit all the fluxes of GJ 758 B. The lack of exploration of metal enrichment in model grids appears as a major limitation that prevents an accurate estimation of the companion physical parameters. The photometry of the new candidate companion is broadly consistent with L-type objects, but a second epoch with improved photometry is necessary to clarify its status. The new astrometry of GJ 758 B shows a significant proper motion since the last epoch. We use this result to improve the determination of the orbital characteristics using two fitting approaches: Least-Squares Monte Carlo and Markov chain Monte Carlo. We confirm the high-eccentricity of the orbit (peak at 0.5), and find a most likely semi-major axis of 46.05 AU. We also use our imaging data, as well as archival radial velocity data, to reject the possibility that this is a false positive effect created by an unseen, closer-in, companion. Finally, we analyze the sensitivity of our data to additional closer-in companions and reject the possibility of other massive brown dwarf companions down to 4–5 AU.
Key words: methods: data analysis / techniques: high angular resolution / techniques: image processing / stars: individual: GJ 758 / brown dwarfs
© ESO, 2016
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