The β Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR^★

¹ LESIA, Observatoire de Paris, Univ. Paris-Cité, Univ. PSL, CNRS, Sorbonne Univ., 5 pl. Jules Janssen, 92195 Meudon, France
e-mail: nour.skaf@obspm.fr
² National Astronomical Observatory of Japan, Subaru Telescope, 650 North A’ohōkū Place, Hilo, HI 96720, USA
³ Department of Physics and Astronomy, University College London Gower Street, WC1E 6BT London, UK
⁴ Université Paris-Saclay, Université Paris Cité CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁵ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁶ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁷ IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France
⁸ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁹ STAR Institute, Université de Liège, Allée du Six Août 19c, 4000 Liège, Belgium
¹⁰ Université de Lyon, Université Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR 5574, 69230 Saint-Genis-Laval, France
¹¹ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹² Laboratoire J.-L. Lagrange, Université Côte d'Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
¹³ Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁴ Astrobiology Center of NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁵ Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
¹⁶ College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USA
¹⁷ Aix-Marseille Univ., CNRS, CNES, LAM, Marseille, France
¹⁸ Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, 221 00 Lund, Sweden
¹⁹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

Received: 5 October 2022
Accepted: 8 March 2023

Abstract

Context. β Pictoris is a young nearby system hosting a well-resolved edge-on debris disk, along with at least two exoplanets. It offers key opportunities for carrying out detailed studies of the evolution of young planetary systems and their shaping soon after the end of the planetary formation phase.

Aims. We analyzed high-contrast coronagraphic images of this system, obtained in the mid-infrared, taking advantage of the NEAR experiment using the VLT/VISIR instrument, which provides access to adaptive optics, as well as phase coronagraphy. The goal of our analysis is to investigate both the detection of the planet β Pictoris b and of the disk features at mid-IR wavelengths. In addition, by combining several epochs of observation, we expect to constrain the position of the known clumps and improve our knowledge on the dynamics of the disk.

Methods. We observed the β Pictoris system over two nights in December 2019 in the 10–12.5 µm coronagraphic filter. To evaluate the planet b flux contribution, we extracted the photometry at the expected position of the planet and compared it to the flux published in the literature. In addition, we used previous data from T-ReCS and VISIR in the mid-IR, updating the star's distance, to study the evolution of the position of the southwest clump that was initially observed in the planetary disk back in 2003.

Results. While we did not detect the planet b, we were able to put constraints on the presence of circumplanetary material, ruling out the equivalent of a Saturn-like planetary ring around the planet. The disk presents several noticeable structures, including the known southwest clump. Using a 16-yr baseline, sampled with five epochs of observations, we were able to examine the evolution of the clump. We found that the clump orbits in a Keplerian motion with a semi-major axis of 56.1_−0.3^+0.4 au. In addition to the known clump, the images clearly show the presence of a second clump on the northeast side of the disk as well as possibly fainter and closer structures that are yet to be confirmed. Furthermore, we found correlations between the CO clumps detected with ALMA and the northeastern and southwestern clumps in the mid-IR images.

Conclusions. If the circumplanetary material were located at the Roche radius, the maximum amount of dust determined from the flux upper limit around β Pictoris b would correspond to the mass of an asteroid of 5 km in diameter. Finally, the Keplerian motion of the southwestern clump is possibly indicative of a yet-to-be detected planet or signals the presence of a vortex.