Resolving the large exoKuiper belt of the HD 126062 debris disc and extended gas emission in its vicinity

TL;DR

This work furnishes the first ALMA characterization of HD 126062's debris disc, revealing a large, narrow exo-Kuiper belt at $R \approx 270$ au and a second inner warm belt at $\sim 22$ au inferred from the SED. Using interferometric visibility fitting, the belt is constrained to be nearly face-on ($i \le 17^\circ$) with $ R$ and width precisely quantified, while the SED modeling ties the outer belt location to the resolved structure and supports a multi-belt architecture. The detection of extended $^{12}$CO (2--1) emission nearby, but largely external to the belt and offset in velocity, suggests the gas is not bound to the HD 126062 system and may originate from a background cloud; this has implications for understanding gas in debris discs around A-type stars. Dynamical analysis indicates that a sub-Jovian planet migrating across the disc could carve the observed gap, offering a plausible planet–disc interaction scenario and a target for future direct-imaging searches. Overall, the study advances our knowledge of giant belt systems around luminous stars and informs models of planet formation and gas evolution in debris discs.

Abstract

Intermediate-mass stars (1-3 Msun) host some of the brightest and best-studied debris discs. This stellar class is also the most frequent host of molecular gas in systems older than typical protoplanetary disc lifetimes, and the most likely to host detected giant planets in radial-velocity surveys. The debris discs of intermediate-mass stars have therefore become fertile ground for studying disc-planet interactions. In this work, we present the first ALMA observations toward the A-type star HD 126062, located in Upper Centaurus Lupus / Lower Centaurus Crux, with the aim of characterising its debris disc. We probed the thermal continuum emission using observations at 1.3 mm, analysed through image reconstruction under different visibility-weighting regimes and parametric model fitting to the observed visibilities. The setup also covered the frequency of the 12CO(2-1) line, allowing imaging of gas near the system. We detected dust continuum emission from an exo-Kuiper belt around HD 126062. Modelled as a Gaussian ring, the visibilities are consistent with a radial separation R = 2.01'' (+0.04, -0.05), equivalent to ~270 (+5, -4) au, and a full width at half maximum DeltaR = 0.71'' +- 0.09 (95 +- 12 au). The continuum emission appears nearly face-on, with inclination <=17 deg. 12CO(2-1) emission is detected in the vicinity of the debris disc, with most of it located external to the exo-Kuiper belt. The exo-Kuiper belt characterised here is among the largest yet detected and agrees with previous predictions of the dust distribution based on spectral energy distribution fitting. The morphology and velocity offset relative to the systemic velocity suggest that the gas is not associated with the star or disc, but likely originates from a diffuse cloud in the nearby galaxy.

Figures (9)

• Figure 1: Top row: On the left is the fiducial image of the continuum observations of HD 126062 reconstructed using tclean with natural weighting. In the middle is the Gaussian ring model derived from the MCMC fit to the visibilities. On the right is the residual image following the subtraction of the model from the data, restored using the same imaging parameters as the tclean image. Bottom row: Same as the top row, except tclean images are reconstructed with a uvtaper of 1$\farcs$5 applied. Contours are drawn in the tclean and residual images at -3,3,4 $\times \sigma_{\rm im}$, where $\sigma_{\rm nat}=$ 25 $\mu$Jy/beam and $\sigma_{\rm taper}=$ 40 $\mu$Jy/beam. Negative contours are shown as dashed lines.
• Figure 2: Fit to the spectral energy distribution of HD 126062, comprised of two blackbody components and a stellar contribution. Error bars are included, but are smaller than the data point markers.
• Figure 3: The integrated intensity (moment-0) map of the $^{12}$CO(2--1) transition observed towards HD 126062. Emission above $3\sigma$ in the channels is used to construct this moment map. White contours show the continuum image constructed with a uvtaper. The beam size is indicated in the lower left corner.
• Figure 4: Top:$^{12}$CO spectra extracted from different regions of the image. Disk region is found within R+$\Delta R$, the external region begins at R+$\Delta R$ and extends as far as 3$\sigma$ emission is detected in the moment 0 map ($\approx 12^{"}$). Total encompasses both these regions. The systemic velocity as measured by gaia is indicated by a vertical line. Bottom: The moment 8 map of $^{12}$CO emission, which collapses the cube in the spectral axis and shows the peak emission for each pixel in the cube.
• Figure 5: exoKuiper belt positions as characterised by the REASONS survey, plotted as a function of the stellar luminosity of their host, where error bars indicate $\Delta R$ as derived by the given references. HD 126062 is also plotted, using the stellar luminosity as derived from the SED fitting in this work. We also plot distance-stellar luminosity relations, $R \propto L^{\alpha}$ fit to samples of discs observed in the mm Matra2019KuiperALMA and far-IR Marshall2021AWavelengths.