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

TL;DR

The paper investigates the inner disc structure around the F-type Herbig Ae/Be star HD 142527 A by combining multi-epoch VLTI interferometry from MATISSE with previous PIONIER and GRAVITY data to probe sub-au to a few-au scales. It employs a parametric, geometrically thin disc model that includes azimuthal asymmetry and an off-centre Gaussian component, constrained by a dust-opacity model derived from the N-band spectrum and analyzed within a Bayesian framework. The analysis reveals time-variable, non-axisymmetric N-band emission with a very close-in inner rim at $R_ ext{in} oughly0.1$ au and an outer disc extending to $r_ ext{out} oughly6$ au, suggesting strong dynamical influence from the nearby companion HD 142527 B. The best-fitting, epoch-dependent model indicates that the inner-disc geometry is complex and likely modulated on yearly timescales, emphasizing the role of the stellar companion in driving disc variability and underscoring the need for dedicated interferometric imaging campaigns to fully map the on-sky brightness distribution.

Abstract

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.

Figures (12)

• Figure 1: Opacity fit. The model (black) is overlaid onto the averaged N-band ut data (orange). Here, the pah flux contribution is excluded from the model curve as is the case for the disc modelling in Sect. \ref{['sec:modelling:modelComponents']}.
• Figure 2: System sketch. The host star HD 142527 A (orange star) orbited by its companion HD 142527 B (blue star at apoapsis). The orbit (blue) was computed using parameters from nowakOrbitHD1425272024. The same parameters were used to derive the positions of the matisse points (teal squares). Bottom right: observation with sphere of the outer disc avenhausExploringDustHD2017 with the orbit (light blue) of the companion indicated.
• Figure 3: Fit to data for the best-fit, one-zone disc model with an off-centre Gaussian asymmetry. The data (colored line) is overlaid with the model (black cross). The residuals of the plots are presented in Fig. \ref{['fig:bestFitResiduals']}. Left: the total spectrum $F_\nu$. Middle: the correlated fluxes $F_{\nu,\text{corr}}$. Right: the closure phases $\Phi_{\nu,\text{cp}}$. Top: the pionier (H band), gravity (K band), and matisse (L and M band) data. This data is fitted with all N-band data sets and shown, as an example, is the fit with the first N-band epoch. Second row to bottom: the first to third N-band epoch (2021, 2022, 2023).
• Figure 4: Model images (in surface brightness). Left to right: the three epochs (2021, 2022, and 2023). Top: the two-zone disc model. Bottom: the best-fit, one-zone disc model plus a Gaussian.
• Figure 5: matisse N-band observations of HD 142527 (Table \ref{['tab:observations']}). Left to right: the baseline distribution, the single dish spectra, the correlated fluxes, and the closure phases.