Dust populations from 30 to 1000 au in the debris disk of HD 120326

Panchromatic view with VLT/SPHERE, ALMA, and HST/STIS

¹ European Southern Observatory, Alonso de Córdova 3107 Vitacura, Santiago, Chile
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble
³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Departamento de Física, Universidad de Santiago de Chile, Av. Victor Jara 3659, Santiago, Chile
⁵ Millennium Nucleus on Young Exoplanets and their Moons (YEMS), Chile
⁶ Center for Interdisciplinary Research in Astrophysics Space Exploration (CIRAS), Universidad de Santiago de Chile, Chile
⁷ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁸ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁹ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, 19 Allée du Six AoÛt, 4000 Liège, Belgium
¹⁰ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹¹ Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
¹² KU Leuven, Institute for Astronomy, Celestijnenlaan 200D, Leuven, Belgium
¹³ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
¹⁴ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK

^★ Corresponding author: celia.desgrange@eso.org

Received: 17 October 2024
Accepted: 7 April 2025

Abstract

Context. To date, more than a hundred debris disks have been spatially resolved. Among them, the young system HD 120326 stands out, displaying different disk substructures on both intermediate (30–150 au) and large (150–1000 au) scales.

Aims. We present new VLT/SPHERE (1.0–1.8 μm) and ALMA (1.3 mm) data of the debris disk around HD 120326. By combining them with archival HST/STIS (0.2–1.0 μm) and archival SPHERE data, we have been able to examine the morphology and photometry of the debris disk, along with its dust properties.

Methods. We present the open-access code MoDiSc (Modeling Disks in Scattered light) to model the inner belt jointly using the SPHERE polarized and total intensity observations. Separately, we modeled the ALMA data and the spectral energy distribution (SED). We combined the results of both these analyses with the STIS data to determine the global architecture of HD 120326.

Results. For the inner belt, identified as a planetesimal belt, we derived a semi-major axis of 43 au, fractional luminosity of 1.8 × 10⁻³, and maximum degree of polarization of 51% ± 6% at 1.6 μm. The spectral slope of its reflectance spectrum is red between 1.0 and 1.3 μm and gray between 1.3 and 1.8 μm. Additionally, the SPHERE data show that there could be a halo of small particles or a second belt at distances ≤150 au. Using ALMA, we derived in the continuum (1.3 mm) an integrated flux of 561 ± 20 μJy. We did not detect any ¹²CO emission. At larger separations (>150 au), we highlight a spiral-like feature spanning hundreds of astronomical units in the STIS data.

Conclusions. Further data are needed to confirm and better constrain the dust properties and global morphology of HD 120326.