First light of the VLT planet finder SPHERE. I. Detection and characterization of the sub-stellar companion GJ 758 B
Creators: name: Vigan, A.
name: Bonnefoy, M.
name: Ginski, C.
name: Beust, H.
name: Galicher, R.
name: Janson, M.
name: Baudino, J. -L.
name: Buenzli, E.
name: Hagelberg, J.
name: D'Orazi, V.
name: Desidera, S.
name: Maire, A. -L.
name: Gratton, R.
name: Sauvage, J. -F.
name: Chauvin, G.
name: Thalmann, C.
name: Malo, L.
name: Salter, G.
name: Zurlo, A.
name: Antichi, J.
name: Baruffolo, A.
name: Baudoz, P.
name: Blanchard, P.
name: Boccaletti, A.
name: Beuzit, J. -L.
name: Carle, M.
name: Claudi, R.
name: Costille, A.
name: Delboulbé, A.
name: Dohlen, K.
name: Dominik, C.
name: Feldt, M.
name: Fusco, T.
name: Gluck, L.
name: Girard, J.
name: Giro, E.
name: Gry, C.
name: Henning, T.
name: Hubin, N.
name: Hugot, E.
name: Jacquet, M.
name: Kasper, M.
name: Lagrange, A. -M.
name: Langlois, M.
name: Mignant, D. Le
name: Llored, M.
name: Madec, F.
name: Martinez, P.
name: Mawet, D.
name: Mesa, D.
name: Milli, J.
name: Mouillet, D.
name: Moulin, T.
name: Moutou, C.
name: Origné, A.
name: Pavlov, A.
name: Perret, D.
name: Petit, C.
name: Pragt, J.
name: Puget, P.
name: Rabou, P.
name: Rochat, S.
name: Roelfsema, R.
name: Salasnich, B.
name: Schmid, H. -M.
name: Sevin, A.
name: Smette, A.
name: Stadler, E.
name: Suarez, M.
name: Turatto, M.
name: Udry, S.
name: Vakili, F.
name: Wahhaj, Z.
name: Weber, L.
name: Wildi, F.
Publisher: name: arXiv
Year: 2015
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: GJ758 B is a brown dwarf companion to a nearby (15.76 pc) 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 (~600K) companion ever directly imaged around a neighboring star. We present new high-contrast data obtained during the commissioning of the SPHERE instrument at the VLT. The data was obtained in Y-, J-, H-, and Ks-bands with the dual-band imaging (DBI) mode of IRDIS, 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 8 photometric points for an extended comparison of GJ758 B with empirical objects and 4 families of atmospheric models. From comparison to empirical object, we estimate a T8 spectral type, but none of the comparison object can accurately represent the observed near-IR fluxes of GJ758 B. From comparison to atmospheric models, we attribute a Teff = 600K $\pm$ 100K, but we find that no atmospheric model can adequately fit all the fluxes of GJ758 B. 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 GJ758 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-Square Monte Carlo and Markov Chain Monte Carlo. 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. [abridged]
description: 20 pages, 15 figures. Accepted for publication in A&amp;A