Astronomy and Astrophysics, volume 651A, 34-34 (2021/7-1)
The HD 206893 planetary system seen with VLT/SPHERE. Upper limit on the dust albedo and constraints on additional companions.
ROMERO C., MILLI J., LAGRANGE A.-M., VAN HOLSTEIN R.G., CANTALLOUBE F., MARINO S. and RAY S.
Abstract (from CDS):
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 ∼25MJup brown dwarf detected at ∼10au 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 180au, with a ∼27au wide gap at ∼74au. 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 2.6au, and we estimate our probability of detection higher than 90% for brown dwarfs more massive than 55MJup in this separation range. At 74au, where a gap is detected in the disk in thermal imaging, this probability of detection corresponds to planets above 2.5MJup. 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.