The HD 206893 planetary system seen with VLT/SPHERE

Upper limit on the dust albedo and constraints on additional companions

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
e-mail: cromero@eso.org
³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁴ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁶ Jesus College, University of Cambridge, Jesus Lane, Cambridge CB5 8BL, UK
⁷ Astrophysics Group, University of Exeter, Physics Building, Stocker Road, Devon EX4 4QL, UK

Received: 24 September 2020
Accepted: 1 April 2021

Abstract

Context. The detection and characterization of planets and debris disks is a very active field in current research. The F5V star HD 206893 hosts a ~25 M_Jup brown dwarf detected at ~10 au in VLT/SPHERE high-contrast images. This system is also known to host a debris disk, which is inferred from its high infrared excess. This disk was recently resolved in thermal submillimeter imaging with ALMA and extends from 30 to 180 au, with a ~27 au wide gap at ~74 au.

Aims. Our goal is to search for the scattered light emission of the disk using the largest amount of SPHERE imaging data available to date. We also want to bring tighter constraints on the presence of additional low-mass companions based on the available multi-epoch high-contrast imaging data.

Methods. We analyzed six epochs of SPHERE near-infrared data, processed with angular, polarimetric, and reference differential imaging, in order to detect the disk around HD 206893.

Results. We do not detect the debris disk. Based on recent constraints on the disk morphology from ALMA data, this non-detection is compatible with a maximum albedo of 0.55 in the H band and 0.96 in the K band. Furthermore, we do not detect additional low-mass companions in the system. A low-mass companion is expected from radial velocity and astrometric measurements between 1.4 and 2.6 au, and we estimate our probability of detection higher than 90% for brown dwarfs more massive than 55 M_Jup in this separation range. At 74 au, where a gap is detected in the disk in thermal imaging, this probability of detection corresponds to planets above 2.5 M_Jup.

Conclusions. The non-detection of the disk through the methods used in this study should not exclude an attempt with other techniques, such as advanced reference-star differential imaging using machine-learning-based libraries or star hopping. Furthermore, the future JWST instrument NIRCam might offer the possibility of detecting the disk in scattered light thanks to its increased sensitivity.