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Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2016

First light of the VLT planet finder SPHERE I. Detection and characterization of the substellar companion GJ 758 B

1 LAM - Laboratoire d'Astrophysique de Marseille
2 ESO - European Southern Observatory [Santiago]
3 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
4 Leiden Observatory [Leiden]
5 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
6 Stockholm University
7 MPIA - Max-Planck-Institut für Astronomie
8 Institute for Astronomy [Honolulu]
9 ObsGE - Observatoire Astronomique de l'Université de Genève
10 OAPD - INAF - Osservatorio Astronomico di Padova
11 Macquarie University
12 Monash University [Melbourne]
13 DOTA, ONERA, Université Paris Saclay (COmUE) [Châtillon]
14 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
15 CFHT - Canada-France-Hawaii Telescope Corporation
16 UDP - Universidad Diego Portales [Santiago - Chili]
17 USACH - Universidad de Santiago de Chile [Santiago]
18 OAA - INAF - Osservatorio Astrofisico di Arcetri
19 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
20 ESO - European Southern Observatory
21 CPPM - Centre de Physique des Particules de Marseille
22 CRAL - Centre de Recherche Astrophysique de Lyon
23 EPOC - Environnements et Paléoenvironnements OCéaniques
24 OCA - Observatoire de la Côte d'Azur
25 CALTECH - California Institute of Technology
26 MONARIS - De la Molécule aux Nanos-objets : Réactivité, Interactions et Spectroscopies
27 NOVA Optical Infrared Instrumentation Group
28 Institut d'Astrophysique et de Géophysique [Liège]
29 LAGRANGE - Joseph Louis LAGRANGE
30 ESRF - European Synchrotron Radiation Facility
31 CREATIS - Centre de Recherche en Acquisition et Traitement de l'Image pour la Santé
S. Desidera
R. Gratton
A. Baruffolo
R. Claudi
K. Dohlen
C. Dominik
E. Giro
C. Gry
T. Henning
E. Hugot
F. Madec
D. Mesa
B. Salasnich
R. Siebenmorgen
M. Turatto

Résumé

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 (similar to 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 K-s-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 T-eff = 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.

Dates et versions

hal-01440124 , version 1 (19-01-2017)

Identifiants

Citer

Arthur Vigan, M. Bonnefoy, C. Ginski, H. Beust, R. Galicher, et al.. First light of the VLT planet finder SPHERE I. Detection and characterization of the substellar companion GJ 758 B. Astronomy and Astrophysics - A&A, 2016, 587, ⟨10.1051/0004-6361/201526465⟩. ⟨hal-01440124⟩
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