JWST/NIRCam observations of HD 92945 debris disk: An asymmetric disk with a gap

¹ INAF, Astronomical Observatory of Padua, Vicolo dell’Osservatorio 5, 35122, Padua, Italy
² Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
³ NASA-Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁴ Space Telescope Science Institute, 3700 San Martin Dr, Baltimore, MD 21218, USA
⁵ Centre for Exoplanets and Habitability, University of Warwick, Coventry CV4 7AL, UK
⁶ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁷ Malaghan Institute of Medical Research, Gate 7, Victoria University, Kelburn Parade, Wellington, New Zealand
⁸ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁹ School of Mathematics and Physics, University of Queensland, St Lucia, QLD 4072, Australia

^★ Corresponding author: cecilia.lazzoni@inaf.it

Received: 20 May 2025
Accepted: 30 October 2025

Abstract

Aims. We present the first observations of the HD 92945 debris disk obtained with the James Webb Space Telescope (JWST), targeting this nearby K0V star located at 21.54 pc from the Sun. The main objectives are to characterize the disk’s morphology in the near infrared, compare it with previous data from ALMA and HST, and place new constraints on the presence and properties of potential planetary companions shaping the disk.

Methods. High-contrast coronagraphic imaging was performed using JWST/NIRCam in the F200W and F444W filters. Advanced postprocessing techniques were employed, including reference differential imaging (RDI) with custom-built point spread function (PSF) libraries, and forward modeling of the disk using synthetic PSFs and MCMC optimization. After subtracting the disk contribution, the residuals were analyzed to identify candidate point sources. From these, we derived contrast curves and constructed detection probability maps for substellar companions.

Results. The disk is clearly detected in both NIRCam filters and reveals a broad, inclined structure with a gap, consistent with previous scattered-light and ALMA observations. The modeling confirms the presence of a gap at ∼80 au and shows a scale height and scattering properties compatible with a dynamically active disk. A significant brightness asymmetry is observed in the southwestern inner ring at both 2 and 4.4 μm, consistent with previous ALMA results. Observing this feature across different wavelengths and epochs strongly supports a scenario where one or more unseen planetary companions are perturbing the disk. No comoving sources are detected, and all candidate objects in the field are consistent with background stars or galaxies. The derived detection limits exclude planets more massive than ∼0.4-0.5 M_Jup beyond 100 au and more massive than ∼1 M_Jup beyond 20-40 au. This, in turn, rules out the possibility of a single planet placed beyond ∼ 20 au as responsible for the astrometric signal observed by Gaia. These results, combined with the observed disk features, support a scenario in which a single or multiple sub-Jupiter planets dynamically shape the system through mechanisms such as secular apsidal resonances, providing a coherent explanation for the gap, the asymmetric brightness distribution and the astrometric signal.