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

TL;DR

This study uses JWST/NIRCam high-contrast imaging to map the HD 92945 debris disk in the near-IR, confirming a broad inclined disk with a gap near ~80 au and a brighter southwestern inner ring. Forward modeling with a ALMA/HST-compatible dust density profile and MCMC fitting yields precise disk geometry ( Rin ≈ 55–59 au, Rout ≈ 97–101 au, i ≈ 63–65°, pa ≈ −79°) and gap properties (rg ≈ 80–81 au, wg ≈ 26–31 au), plus a higher near-IR scale height than submillimeter measurements. Contrast curves and detection probability maps show that JWST can exclude Jupiter-mass planets beyond ~20–40 au at high confidence and place stringent limits near the gap, while PMa constraints imply possible interior companions (2.5–20 au) capable of producing the observed astrometric signal; a single outer planet cannot be ruled out, but a two-planet secular resonance scenario remains a compelling explanation for the gap and asymmetry. Overall, the work demonstrates JWST’s power to jointly characterize disk structure and constrain planetary architectures in debris-disk systems, guiding future multiwavelength imaging and dynamical modeling.

Abstract

We present the first observations of the HD92945 debris disk obtained with JWST, targeting this nearby K0V star located at 21.54 pc from the Sun. High-contrast coronagraphic imaging was performed using JWST/NIRCam in the F200W and F444W filters. After subtracting the disk contribution through forward modeling by means of synthetic PSFs and MCMC optimizations, the residuals were analyzed to identify candidate point sources. From these, we derived contrast curves and constructed detection probability maps for substellar companions. 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 MJ beyond 100 au and more massive than ~1 MJ 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.

Figures (12)

• Figure 1: NIRCam reductions for HD 92945 for the F444W (left panel) and the F200W (right panel) filters. Both images where obtained performing RDI with HD 92921 as reference. The images are rotated to northeast, with the scale bar in the bottom left corner representing a projected distance of 50 au.
• Figure 2: F200W data, model, and residuals of HD 92945's disk using one reference, HD 92921, (top panels) and the PSF library considering the entire image (second row) or excluding the bright regions close to the minor axis (last row).
• Figure 3: Smoothed images of the residuals obtained after modeling and subtracting the disk in the F444W (left panel) and F200W (right panel) filters. The disk luminosity asymmetry detected in both filters in the west portion of the disk is pointed by the arrow. For the both filters, we also added the $2\times10^{-4}$ Jy/beam contour level from ALMA data Marino2.
• Figure 4: From left to right, F444W data, model, and residuals of HD 92945's disk using: a) the same morphological parameters adopted for the disk as seen at 2 $\mu$m and one reference, HD 92921, (first row) or the PSF library (second row); b) the same morphological parameters adopted at 2 $\mu$m with the exception of $l_{out}$, optimized for these data, using the same single reference, (mid-bottom panels) or the PSF library (bottom panels)
• Figure 5: Radial density distribution of the dust obtained from PSF libray+mask modeling of F200W and F444W JWST data (dark blue and light blue curves) and comparison with ALMA (pink curves) and HST (green curve). For F200W JWST filter and ALMA, the solid line represents the median, while the shaded areas represent the 68, 95, and 99.7 per cent confidence regions as obtained by Marino3. F444W JWST profile was obtained using the mean parameters derived at 2 $\mu$m (column four of Table \ref{['tabdisk']}), with the exception of $l_{\rm out}$, set at 30. For HST, the curve is taken from Fig. 7 of Golimowski.