Letter to the Editor

Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk^⋆

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail amueller@mpia.de
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS/INSU UMI 3386 and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
⁴ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 9219 Meudon, France
⁵ Department of Physics, University of Oxford, Oxford, UK
⁶ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
⁷ Geneva Observatory, University of Geneva, Chemin des Mailettes 51, 1290 Versoix, Switzerland
⁸ INAF–Osservatorio Astronomico di Padova, Vicolo della Osservatorio 5, 35122 Padova, Italy
⁹ DOTA, ONERA, Université Paris Saclay, 91123 Palaiseau, France
¹⁰ Aix Marseille Université, CNRS, Laboratoire d’Astrophysique de Marseille (LAM) UMR 7326, 13388 Marseille, France
¹¹ Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
¹² Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
¹³ Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
¹⁴ CRAL, UMR 5574, CNRS, Université de Lyon, Ecole Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France
¹⁵ INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
¹⁶ INCT-Universidad De Atacama, calle Copayapu 485, Copiapó Atacama, Chile
¹⁷ Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109-1107, USA
¹⁸ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁹ Physikalisches Institut, Universität Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²⁰ Konkoly Observatory Research, Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary
²¹ Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, UMR 7326, 13388 Marseille, France
²² European Southern Observatory (ESO), Alonso de Còrdova 3107, Vitacura, Casilla 19001, Santiago, Chile
²³ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
²⁴ Escuela de Ingeniería Industrial, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile

Received: 6 June 2018
Accepted: 8 July 2018

Abstract

Context. The observation of planets in their formation stage is a crucial but very challenging step in understanding when, how, and where planets form. PDS 70 is a young pre-main sequence star surrounded by a transition disk, in the gap of which a planetary-mass companion has recently been discovered. This discovery represents the first robust direct detection of such a young planet, possibly still at the stage of formation.

Aims. We aim to characterize the orbital and atmospheric properties of PDS 70 b, which was first identified on May 2015 in the course of the SHINE survey with SPHERE, the extreme adaptive-optics instrument at the VLT.

Methods. We obtained new deep SPHERE/IRDIS imaging and SPHERE/IFS spectroscopic observations of PDS 70 b. The astrometric baseline now covers 6 yr, which allowed us to perform an orbital analysis. For the first time, we present spectrophotometry of the young planet which covers almost the entire near-infrared range (0.96–3.8 μm). We use different atmospheric models covering a large parameter space in temperature, log g, chemical composition, and cloud properties to characterize the properties of the atmosphere of PDS 70 b.

Results. PDS 70 b is most likely orbiting the star on a circular and disk coplanar orbit at ~22 au inside the gap of the disk. We find a range of models that can describe the spectrophotometric data reasonably well in the temperature range 1000–1600 K and log g no larger than 3.5 dex. The planet radius covers a relatively large range between 1.4 and 3.7 R_J with the larger radii being higher than expected from planet evolution models for the age of the planet of 5.4 Myr.

Conclusions. This study provides a comprehensive data set on the orbital motion of PDS 70 b, indicating a circular orbit and a motion coplanar with the disk. The first detailed spectral energy distribution of PDS 70 b indicates a temperature typical of young giant planets. The detailed atmospheric analysis indicates that a circumplanetary disk may contribute to the total planetflux.