VLT/SPHERE astrometric confirmation and orbital analysis of the brown dwarf companion HR 2562 B^★

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: maire@mpia.de
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Via Marzolo, 8, 35121 Padova, Italy
⁵ LESIA, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Paris 6, Sorbonne Université, 5 place J. Janssen, 92195 Meudon, France
⁶ INCT, Universidad de Atacama, calle Copayapu 485, Copiapó, Atacama, Chile
⁷ Unidad Mixta Internacional Franco-Chilena de Astronomía CNRS/INSU UMI 3386 and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
⁸ Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
⁹ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
¹⁰ Núcleo Milenio Formación Planetaria - NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
¹¹ ETH Zurich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
¹² CRAL, UMR 5574, CNRS/ENS-Lyon/Université Lyon 1, 9 avenue Charles André, 69561 Saint-Genis-Laval, France
¹³ Aix-Marseille Univ., CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
¹⁴ Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109-1107, USA
¹⁵ INAF – Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (LC), Italy
¹⁶ Geneva Observatory, University of Geneva, Chemin des Maillettes 51, 1290 Versoix, Switzerland
¹⁷ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Avenida Ejército 441, Santiago, Chile
¹⁸ Millennium Nucleus “Protoplanetary Disk”, Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹⁹ Université Côte d’Azur, OCA, CNRS, Lagrange, France
²⁰ DOTA, ONERA, Université Paris Saclay, 91123 Palaiseau, France
²¹ Anton Pannekoek Institute for Astronomy, Science Park 904, 1098 XH Amsterdam, The Netherlands

Received: 15 December 2017
Accepted: 9 April 2018

Abstract

Context. A low-mass brown dwarf has recently been imaged around HR 2562 (HD 50571), a star hosting a debris disk resolved in the far infrared. Interestingly, the companion location is compatible with an orbit coplanar with the disk and interior to the debris belt. This feature makes the system a valuable laboratory to analyze the formation of substellar companions in a circumstellar disk and potential disk-companion dynamical interactions.

Aims. We aim to further characterize the orbital motion of HR 2562 B and its interactions with the host star debris disk.

Methods. We performed a monitoring of the system over ~10 months in 2016 and 2017 with the VLT/SPHERE exoplanet imager.

Results. We confirm that the companion is comoving with the star and detect for the first time an orbital motion at high significance, with a current orbital motion projected in the plane of the sky of 25 mas (~0.85 au) per year. No orbital curvature is seen in the measurements. An orbital fit of the SPHERE and literature astrometry of the companion without priors on the orbital plane clearly indicates that its orbit is (quasi-)coplanar with the disk. To further constrain the other orbital parameters, we used empirical laws for a companion chaotic zone validated by N-body simulations to test the orbital solutions that are compatible with the estimated disk cavity size. Non-zero eccentricities (>0.15) are allowed for orbital periods shorter than 100 yr, while only moderate eccentricities up to ~0.3 for orbital periods longer than 200 yr are compatible with the disk observations. A comparison of synthetic Herschel images to the real data does not allow us to constrain the upper eccentricity of the companion.