The asymmetric structure of the inner disc around HD 142527 A with VLTI/MATISSE

Circumstellar discs, and especially their inner regions, covering ranges from <1 au to a few astronomical units, are the birthplaces of terrestrial planets. The inner regions are thought to be similarly diverse in structure as the well-observed outer regions probed by ALMA. Combining data and results from previous studies of the VLTI/PIONIER and VLTI/GRAVITY instruments with new, multi-epoch VLTI/MATISSE observations, we aim to provide a comprehensive picture of the structure of the inner regions of the circumstellar disc around the F-type Herbig Ae/Be star HD 142527 A, the primary of a binary star system. We model the multi-wavelength interferometric data using a parametrised, geometrically thin disc model, allowing for azimuthal asymmetry, exploring a first-order disc modulation and an off-centre Gaussian component. We find time-variable structures in the N-band observables, which we reproduce with time-dependent models. This variability manifests as azimuthally asymmetric emission, evidenced by strong, non-zero closure phases in the N-band data. Fits to individual epochs of the N-band observations yield better $χ^2_\text{r}$ values than fits to all epochs simultaneously. This suggests substantial changes in the geometry of the inner disc emission from ~1 au up to a few astronomical-unit scales from one year to the next. Moreover, our models produce a very close-in inner disc rim $R_\text{rim}\approx0.1$ au. All together, we find a very complex, substantially non-point symmetric and temporally-variable disc ($r_\text{out}\lesssim6$ au) around the primary. The very close-in inner rim indicates the presence of material inside the typical wall-like sublimation radius $R_\text{rim,literature}\approx0.3$ au. The complex, temporally variable inner-disc geometry is likely affected or even caused by the close passing (~5 au) and short orbit ($P\approx24$ yr) of the companion HD 142527 B.

💡 Research Summary

The paper presents a multi‑epoch interferometric study of the inner circum‑stellar disc around the Herbig Ae/Be star HD 142527 A, the primary of a close binary system. By combining new VLTI/MATISSE observations (L/M and N bands, 2021‑2023, eight epochs) with previously published VLTI/PIONIER (H‑band) and VLTI/GRAVITY (K‑band) data, the authors achieve a wavelength‑spanning view of the disc from sub‑au to a few astronomical units.

MATISSE’s long baselines (10‑130 m) deliver angular resolutions of ~30 mas at 3 µm and ~10 mas at 12 µm, sufficient to resolve structures out to ~6 au at the distance of 159 pc. The data reduction uses a modified version of the MATISSE pipeline that employs a 2‑D Fourier transform of the interferograms, improving the estimation of correlated fluxes and differential phases. The authors retain the non‑chopping mode for interferometric observables to preserve phase stability.

The N‑band results are the most striking. Correlated fluxes decrease with baseline length but remain at ~0.6 Jy on the longest baselines, indicating compact emission within a few au. Closure phases are large (up to ~47°) and vary significantly between epochs, revealing strong azimuthal asymmetries and a clear temporal variability on a yearly timescale. The total spectra show classic silicate features (including a prominent 11.3 µm forsterite peak) with ~10 % flux variations across epochs, consistent with archival WISE, ISO, and Spitzer measurements.

To interpret the data, the authors adopt a geometrically thin disc model with three key components: (i) a radial brightness profile, (ii) a first‑order azimuthal modulation, and (iii) an off‑centre Gaussian “blob” that captures localized asymmetry. Model fitting is performed via MCMC for each epoch separately and for all epochs simultaneously. The epoch‑by‑epoch fits achieve substantially lower reduced χ² values, demonstrating that a single static geometry cannot reproduce the observations.

Best‑fit parameters point to a very compact inner rim at R₍rim₎≈0.1 au—significantly inside the canonical dust sublimation radius (~0.3 au) for a 6500 K star—suggesting the presence of refractory dust or gas inside the usual sublimation front. The outer edge of the emitting region is constrained to r₍out₎≲6 au. The azimuthal modulation amplitude and the position of the off‑centre Gaussian change from epoch to epoch, indicating that the asymmetry rotates or evolves on a timescale of about one year.

The authors argue that the observed variability is driven by the close, eccentric companion HD 142527 B (M2 type, orbital semi‑major axis 5‑15 au, eccentricity ≈0.5, period ≈24 yr). As B passes near periastron, its gravitational perturbation can excite spiral density waves, warp the inner disc, and funnel material inward, producing the observed non‑point‑symmetric brightness distribution. The timing of the strongest asymmetry aligns with the companion’s periastron passages inferred from orbital solutions, supporting this scenario.

In summary, the study reveals that the inner disc of HD 142527 A is (1) extremely compact (inner rim at 0.1 au), (2) extended out to ~6 au, (3) markedly non‑axisymmetric, and (4) temporally variable on yearly scales. The variability is most plausibly linked to dynamical interactions with the close binary companion. This work demonstrates the power of VLTI/MATISSE, especially when combined with shorter‑wavelength interferometry, to probe the three‑dimensional, time‑dependent structure of planet‑forming zones within a few astronomical units of young stars. The findings have broad implications for theories of disc evolution in binary systems and for the early stages of planet formation under strong dynamical perturbations.