The GRAVITY young stellar object survey

VI. Mapping the variable inner disk of HD 163296 at sub-au scales

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: jsanchez@mpia.de
² Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70264, Ciudad de México, 04510, Mexico
e-mail: joelsb@astro.unam.mx
³ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, D02 XF86 Dublin, Ireland
⁴ School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
⁵ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁶ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁷ Universidade do Porto - Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
⁸ CENTRA, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
⁹ Unidad Mixta Internacional Franco-Chilena de Astronomía (CNRS UMI 3386), Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
¹⁰ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, France
¹¹ Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, 85741 Garching bei München, Germany
¹² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

Received: 6 October 2020
Accepted: 5 July 2021

Abstract

Context. Protoplanetary disks drive some of the formation process (e.g., accretion, gas dissipation, formation of structures) of stars and planets. Understanding such physical processes is one of the most significant astrophysical questions. HD 163296 is an interesting young stellar object for which infrared and sub-millimeter observations have shown a prominent circumstellar disk with gaps plausibly created by forming planets.

Aims. This study aims to characterize the morphology of the inner disk in HD 163296 with multi-epoch, near-infrared interferometric observations performed with GRAVITY at the Very Large Telescope Interferometer. Our goal is to depict the K-band (λ₀ ~ 2.2 μm) structure of the inner rim with milliarcsecond (sub-au) angular resolution. Our data is complemented with archival Precision Integrated-Optics Near-infrared Imaging ExpeRiment (H-band; λ₀ ~ 1.65 μm) data of the source.

Methods. We performed a gradient descent parametric model fitting to recover the sub-au morphology of our source.

Results. Our analysis shows the existence of an asymmetry in the disk surrounding the central star of HD 163296. We confirm variability of the disk structure in the inner ~2 mas (0.2 au). While variability of the inner disk structure in this source has been suggested by previous interferometric studies, this is the first time that it is confirmed in the H- and K-bands by using a complete analysis of the closure phases and squared visibilities over several epochs. Because of the separation from the star, position changes, and the persistence of this asymmetric structure on timescales of several years, we argue that it is probably a dusty feature (e.g., a vortex or dust clouds) made by a mixing of silicate and carbon dust and/or refractory grains, inhomogeneously distributed above the mid-plane of the disk.