MIRI-JWST mid-infrared direct imaging of the debris disk of HD 106906

Structure and mass of the disk

¹ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Sorbonne Paris Cité, CY Cergy Paris Université, CNRS, 5 place Jules Janssen, 92195 Meudon, France
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Department of Physics & Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
⁴ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁵ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁶ HFML – FELIX. Radboud University PO box 9010, 6500 GL Nijmegen, The Netherlands
⁷ SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
⁸ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁹ Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
¹¹ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
¹² STAR Institute, Université de Liège, Allée du Six Août 19c, 4000 Liège, Belgium
¹³ Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹⁴ School of Physics & Astronomy, Space Park Leicester, University of Leicester, 92 Corporation Road, Leicester, LE4 5SP, UK
¹⁵ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁶ Université Paris-Saclay, CEA, IRFU, 91191, Gif-sur-Yvette, France
¹⁷ Department of Astrophysics, American Museum of Natural History, New York, NY 10024, USA
¹⁸ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA
¹⁹ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
²⁰ Department of Astronomy, Oskar Klein Centre, Stockholm University, 106 91 Stockholm, Sweden
²¹ School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin, D02 XF86, Ireland

^★ Corresponding author: daniel.rouan@obspm.fr

Received: 19 September 2024
Accepted: 30 March 2025

Abstract

Context. We report MIRI-JWST coronagraphic observations at 11.3 and 15.5 μm of the debris disk around the young star HD 106906. The wavelength range is sensitive to the thermal emission of the dust heated by the central star.

Aims. The observations were made to characterize the structure of the disk through the thermal emission, to search for clues to the presence of a central void of dust particles, and to derive the mass of the dust and the temperature distribution. Another goal was also to constrain the size distribution of the grains.

Methods. The data were reduced and calibrated using the JWST pipeline. The analysis was based on a forward-modeling of the images using a multiparameter radiative transfer model coupled to an optical code for coronagraphy processing.

Results. The disk is clearly detected at both wavelengths. The slight asymmetry is geometrically consistent with the asymmetry observed in the near-IR, but it is inconsistent the brightness distribution. The observed structure is well reproduced with a model of a disk (or belt) with a critical radius 70 au, a mildly inward-increasing density (index 2) and a steeper decrease outward (index −6). This indication of a filled disk inside the critical radius is inconsistent with sculpting from an inner massive planet. The size distribution of the grains that cause the mid-IR emission is well constrained by the flux ratio at the two wavelengths : 0.45–10 and 0.65–10 μm for silicate and graphite grains, respectively. The minimum size is consistent with predictions of blowout through radiative pressure.

Conclusions. We derive a mass of the dust that causes the mid-IR emission of 3.3–5.0 10⁻³ M_⊕. When the larger grains (up to 1 cm) that cause the millimeter emission are included, we extrapolate this mass to 0.10–0.16 M_⊕. We point out to that this is fully consistent with ALMA observations of the disk in terms of dust mass and of its millimeter flux. We estimate the average dust temperature in the planetesimal belt to be 74 K, but the temperature range within the whole disk is rather wide: from 40 to 130 K.