First resolved observations of a highly asymmetric debris disc around HD 160305 with VLT/SPHERE^★,★★

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
e-mail: clement.perrot@obspm.fr
² Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
³ Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
⁴ CNRS, IPAG, Université Grenoble Alpes, 38000 Grenoble, France
⁵ CNRS, CNES, LAM, Aix-Marseille University, Marseille, France
⁶ INAF – Osservatorio Astronomico di Padova, Vicolo dell Osservatorio 5, 35122 Padova, Italy
⁷ INAF – Osservatorio Astrofisico di Catania, Via S.Sofia 78, 95123 Catania, Italy
⁸ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁹ Institute for Astronomy, University of Edinburgh, EH9 3HJ, Edinburgh, UK
¹⁰ Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
¹¹ Unidad Mixta Internacional Franco-Chilena de Astronomía, CNRS/INSU UMI 3386 and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹² Geneva Observatory, University of Geneva, Chemin des Mailettes 51, 1290 Versoix, Switzerland
¹³ Université Côte d’Azur, OCA, CNRS, Lagrange, France
¹⁴ CRAL, CNRS, Université Lyon 1, ENS, 9 avenue Charles André, 69561 Saint Genis Laval, France
¹⁵ STAR Institute, University of Liège, Allée du Six Août 19c, 4000 Liège, Belgium
¹⁶ INCT, Universidad De Atacama, calle Copayapu 485, Copiapò, Atacama, Chile
¹⁷ DOTA, ONERA, Université Paris Saclay, 91123 Palaiseau, France

Received: 19 November 2018
Accepted: 15 April 2019

Abstract

Context. Direct imaging of debris discs gives important information about their nature, their global morphology, and allows us to identify specific structures possibly in connection with the presence of gravitational perturbers. It is the most straightforward technique to observe planetary systems as a whole.

Aims. We present the first resolved images of the debris disc around the young F-type star HD 160305, detected in scattered light using the VLT/SPHERE instrument in the near infrared.

Methods. We used a post-processing method based on angular differential imaging and synthetic images of debris discs produced with a disc modelling code (GRaTer) to constrain the main characteristics of the disc around HD 160305. All of the point sources in the field of the IRDIS camera were analysed with an astrometric tool to determine whether they are bound objects or background stars.

Results. We detect a very inclined (~82°) ring-like debris disc located at a stellocentric distance of about 86 au (deprojected width ~27 au). The disc displays a brightness asymmetry between the two sides of the major axis, as can be expected from scattering properties of dust grains. We derive an anisotropic scattering factor g > 0.5. A second right-left asymmetry is also observed with respect to the minor axis. We measure a surface brightness ratio of 0.73 ± 0.18 between the bright and the faint sides. Because of the low signal-to-noise ratio (S/N) of the images we cannot easily discriminate between several possible explanations for this left-right asymmetry, such as perturbations by an unseen planet, the aftermath of the breakup of a massive planetesimal, or the pericenter glow effect due to an eccentric ring. Two epochs of observations allow us to reject the companionship hypothesis for the 15 point sources present in the field.