First light of the VLT planet finder SPHERE

II. The physical properties and the architecture of the young systems PZ Telescopii and HD 1160 revisited^⋆

¹ INAF−Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
e-mail: annelise.maire@oapd.inaf.it
² Université Grenoble Alpes, IPAG, 38000 Grenoble, France
e-mail: mickael.bonnefoy@obs.ujf-grenoble.fr
³ CNRS, IPAG, 38000 Grenoble, France
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: ginski@strw.leidenuniv.nl
⁵ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: arthur.vigan@lam.fr
⁶ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001 Vitacura, Santiago 19, Chile
⁷ INAF Catania Astrophysical Observatory, via S. Sofia 78, 95123 Catania, Italy
e-mail: sergio.messina@oact.inaf.it
⁸ LESIA, CNRS, Observatoire de Paris, Université Paris Diderot, UPMC, 5 place J. Janssen, 92190 Meudon, France
⁹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ International Max Planck Research School for Astronomy and Space Physics, 69117 Heidelberg, Germany
¹¹ York Creek Observatory, Georgetown, Tasmania, Australia
¹² Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
¹³ Geneva Observatory, University of Geneva, Chemin des Maillettes 51, 1290 Versoix, Switzerland
¹⁴ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
¹⁵ Millennium Nucleus “Protoplanetary Disk”, Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹⁶ INAF−Osservatorio Astrofisico di Arcetri, largo E. Fermi 5, 50125 Firenze, Italy
¹⁷ INAF−Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁸ Anton Pannekoek Astronomical Institute, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, The Netherlands
¹⁹ ONERA, The French Aerospace Lab BP72, 29 avenue de la Division Leclerc, 92322 Châtillon Cedex, France
²⁰ Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
²¹ European Southern Observatory, Karl Schwarzschild St, 2, 85748 Garching, Germany
²² Centre de Recherche Astrophysique de Lyon, CNRS/ENS-L/Université Lyon 1, 9 av. Ch. André, 69561 Saint-Genis-Laval, France
²³ Laboratoire Lagrange, UMR 7293, Observatoire de la Côte d’Azur (OCA), Université de Nice-Sophia Antipolis (UNS), CNRS, Bd. de l’Observatoire, 06304 Nice, France
²⁴ Department of Astronomy, California Institute of Technology, 1200 E. California Blvd, MC 249-17, Pasadena, CA 91125, USA
²⁵ CNRS, Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy., Kamuela, HI-96743, USA
²⁶ NOVA Optical-Infrared Instrumentation Group at ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

Received: 25 May 2015
Accepted: 13 October 2015

Abstract

Context. The young systemsPZ Tel and HD 1160, hosting known low-mass companions, were observed during the commissioning of the new planet finder of the Very Large Telescope (VLT) SPHERE with several imaging and spectroscopic modes.

Aims. We aim to refine the physical properties and architecture of both systems.

Methods. We use SPHERE commissioning data and dedicated Rapid Eye Mount (REM) observations, as well as literature and unpublished data from VLT/SINFONI, VLT/NaCo, Gemini/NICI, and Keck/NIRC2.

Results. We derive new photometry and confirm the short-term (P = 0.94 d) photometric variability of the star PZ Tel A with values of 0.14 and 0.06 mag at optical and near-infrared wavelengths, respectively. We note from the comparison to literature data spanning 38 yr that the star also exhibits a long-term variability trend with a brightening of ~0.25 mag. The 0.63−3.8 μm spectral energy distribution of PZ Tel B (separation ~25 AU) allows us to revise its physical characteristics: spectral type M7 ± 1, T_eff = 2700 ± 100 K, log(g) < 4.5 dex, luminosity log(L/L_⊙) = −2.51 ± 0.10 dex, and mass 38−72 M_J from “hot-start” evolutionary models combining the ranges of the temperature and luminosity estimates. The 1−3.8 μm SED of HD 1160 B (~85 au) suggests a massive brown dwarf or a low-mass star with spectral type M6.0^+1.0_-0.5, T_eff = 3000 ± 100 K, subsolar metallicity [M/H] = −0.5−0.0 dex, luminosity log(L/L_⊙) = −2.81 ± 0.10 dex, and mass 39−166 M_J. The physical properties derived for HD 1160 C (~560 au) from K_sL′-band photometry are consistent with the discovery study. The orbital study of PZ Tel B confirms its deceleration and the high eccentricity of its orbit (e > 0.66). For eccentricities below 0.9, the inclination, longitude of the ascending node, and time of periastron passage are well constrained. In particular, both star and companion inclinations are compatible with a system seen edge-on. Based on “hot-start” evolutionary models, we reject other brown dwarf candidates outside 0.25′′ for both systems, and giant planet companions outside 0.5′′ that are more massive than 3 M_J for the PZ Tel system. We also show that K1−K2 color can be used along with YJH low-resolution spectra to identify young L-type companions, provided high photometric accuracy (≤0.05 mag) is achieved.

Conclusions. SPHERE opens new horizons in the study of young brown dwarfs and giant exoplanets using direct imaging thanks to high-contrast imaging capabilities at optical (0.5−0.9 μm) and near-infrared (0.95−2.3 μm) wavelengths, as well as high signal-to-noise spectroscopy in the near-infrared domain (0.95−2.3 μm) from low resolutions (R ~ 30−50) to medium resolutions (R ~ 350).