Spectral and orbital characterisation of the directly imaged giant planet HIP 65426 b^★

¹ Département d’Astronomie, Université de Genève, 51 chemin des Maillettes, 1290, Versoix, Switzerland
e-mail: anthony.cheetham@unige.ch
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁴ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁵ Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS/INSU UMI 3386 and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
⁶ Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
⁷ Space Telescope Science Institute, 3700 San Martin Dr. Baltimore, MD 21218, USA
⁸ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
⁹ Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
¹⁰ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
¹¹ Department of Physics and Astronomy, Centre for Planetary Science and Exploration, The University of Western Ontario, London, ON N6A 3K7, Canada
¹² Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA
¹³ Astrophysics Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
¹⁴ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Université Paris 06, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
¹⁵ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691, Stockholm, Sweden
¹⁶ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹⁷ CRAL, UMR 5574, CNRS, Université de Lyon, Ecole Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France
¹⁸ INAF – Osservatorio Astronomico di Padova, Vicolo dell’ Osservatorio 5, 35122, Padova, Italy
¹⁹ INCT, Universidad De Atacama, calle Copayapu 485, Copiapó, Atacama, Chile
²⁰ Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109-1107, USA
²¹ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
²² Escuela de Ingeniería Industrial, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile

Received: 20 August 2018
Accepted: 18 December 2018

Abstract

HIP 65426 b is a recently discovered exoplanet imaged during the course of the SPHERE-SHINE survey. Here we present new L′ and M′ observations of the planet from the NACO instrument at the VLT from the NACO-ISPY survey, as well as a new Y –H spectrum and K-band photometry from SPHERE-SHINE. Using these data, we confirm the nature of the companion as a warm, dusty planet with a mid-L spectral type. From comparison of its SED with the BT-Settl atmospheric models, we derive a best-fit effective temperature of T_eff = 1618 ± 7 K, surface gravity log g = 3.78_−0.03^+0.04 and radius R = 1.17 ± 0.04R_J (statistical uncertainties only). Using the DUSTY and COND isochrones we estimate a mass of 8 ± 1M_J. Combining the astrometric measurements from our new datasets and from the literature, we show the first indications of orbital motion of the companion (2.6σ significance)and derive preliminary orbital constraints. We find a highly inclined orbit (i = 1.07₋₁₀⁺¹³ deg) with an orbital period of 800₋₄₀₀⁺¹²⁰⁰ yr. We also report SPHERE sparse aperture masking observations that investigate the possibility that HIP 65426 b was scattered onto its current orbit by an additional companion at a smaller orbital separation. From this data we rule out the presence of brown dwarf companions with masses greater than 16 M_J at separations larger than 3 AU, significantly narrowing the parameter space for such a companion.