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

Vigan, A. and Mawet, D. (2016) First light of the VLT planet finder SPHERE I. Detection and characterization of the substellar companion GJ 758B. Astronomy and Astrophysics, 587 . Art. No. A55. ISSN 0004-6361. doi:10.1051/0004-6361/201526465.

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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 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.

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URLURL TypeDescription Paper
Vigan, A.0000-0002-5902-7828
Mawet, D.0000-0002-8895-4735
Additional Information:© 2016 ESO. Received 4 May 2015. Accepted 5 November 2015. A.V., M.B., G.C., G.S., J.-L.B., and D.M. acknowledge support in France from the French National Research Agency (ANR) through project grant ANR10-BLANC0504-01, the CNRS-D2P PICS grant, and the Programmes Nationaux de Planétologie et de Physique Stellaire (PNP & PNPS). J.-L.Ba.’s Ph.D is funded by the LabEx Exploration Spatiale des Environnements Planétaires (ESEP) #2011-LABX-030. V.D. is partially supported by the Australian Research Council. V.D., S.D., A.L.M., R.G., and D.M. acknowledge support from the Progetti Premiali funding scheme of the Italian Ministry of Education, University, and Research. E.B. and J.H. are supported by the Swiss National Science Foundation (SNSF). A.Z. acknowledges support from the Millennium Science Initiative (Chilean Ministry of Economy), through grant Nucleus RC130007. The authors warmly thank A. Bellini and J. Anderson for kindly providing the catalog positions of the stars in the 47 Tuc field before their publication. We are very grateful to D. Kirkpatrick, A. Burgasser, D. Pinfield, B. Burningham, and G. Mace for sending us the spectra of benchmark T–Y objects. We thank C. Morley, D. Saumon, and F. Allard for free online access to their atmospheric model grids, and F. Bouchy for his help with the ELODIE data. This research has benefitted from the SpeX Prism Spectral Libraries, maintained by Adam Burgasser at This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. SPHERE is an instrument designed and built by a consortium consisting of IPAG (Grenoble, France), MPIA (Heidelberg, Germany), LAM (Marseille, France), LESIA (Paris, France), Laboratoire Lagrange (Nice, France), INAF – Osservatorio di Padova (Italy), Observatoire de Genève (Switzerland), ETH Zurich (Switzerland), NOVA (Netherlands), ONERA (France) and ASTRON (Netherlands), in collaboration with ESO. SPHERE was funded by ESO, with additional contributions from CNRS (France), MPIA (Germany), INAF (Italy), FINES (Switzerland), and NOVA (Netherlands). SPHERE also received funding from the European Commission Sixth and Seventh Framework Programmes as part of the Optical Infrared Coordination Network for Astronomy (OPTICON) under grant number RII3-Ct-2004-001566 for FP6 (2004–2008), grant number 226604 for FP7 (2009–2012), and grant number 312430 for FP7 (2013–2016).
Funding AgencyGrant Number
Agence Nationale pour la Recherche (ANR)ANR10-BLANC0504-01
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Programmes Nationaux de Planétologie et de Physique Stellaire (PNP & PNPS)UNSPECIFIED
LabEx Exploration Spatiale des Environnements Planétaires (ESEP)2011-LABX-030
Australian Research CouncilUNSPECIFIED
Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR)UNSPECIFIED
Swiss National Science Foundation (SNSF)UNSPECIFIED
Millennium Science Initiative (Chilean Ministry of Economy)Nucleus RC130007
European Southern Observatory (ESO)UNSPECIFIED
Max Planck Institute for Astronomy (MPIA)UNSPECIFIED
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
European Commission Sixth and Seventh Framework ProgrammesRII3-Ct-2004-001566 (OPTICON)
European Research Council (ERC)226604
European Research Council (ERC)312430 (OPTICON)
Subject Keywords:methods: data analysis – techniques: high angular resolution – techniques: image processing – stars: individual: GJ 758 – brown dwarfs
Record Number:CaltechAUTHORS:20160503-091027766
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Official Citation:First light of the VLT planet finder SPHERE - I. Detection and characterization of the substellar companion GJ 758 B A. Vigan, M. Bonnefoy, C. Ginski, H. Beust, R. Galicher, M. Janson, J.-L. Baudino, E. Buenzli, J. Hagelberg, V. D’Orazi, S. Desidera, A.-L. Maire, R. Gratton, J.-F. Sauvage, G. Chauvin, C. Thalmann, L. Malo, G. Salter, A. Zurlo, J. Antichi, A. Baruffolo, P. Baudoz, P. Blanchard, A. Boccaletti, J.-L. Beuzit, M. Carle, R. Claudi, A. Costille, A. Delboulbé, K. Dohlen, C. Dominik, M. Feldt, T. Fusco, L. Gluck, J. Girard, E. Giro, C. Gry, T. Henning, N. Hubin, E. Hugot, M. Jaquet, M. Kasper, A.-M. Lagrange, M. Langlois, D. Le Mignant, M. Llored, F. Madec, P. Martinez, D. Mawet, D. Mesa, J. Milli, D. Mouillet, T. Moulin, C. Moutou, A. Origné, A. Pavlov, D. Perret, C. Petit, J. Pragt, P. Puget, P. Rabou, S. Rochat, R. Roelfsema, B. Salasnich, H.-M. Schmid, A. Sevin, R. Siebenmorgen, A. Smette, E. Stadler, M. Suarez, M. Turatto, S. Udry, F. Vakili, Z. Wahhaj, L. Weber and F. Wildi A&A, 587 (2016) A55 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66611
Deposited On:03 May 2016 17:42
Last Modified:11 Nov 2021 00:00

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