The MATISSE view of the inner region of the RY Tau protoplanetary disk

TL;DR

This study uses MATISSE VLTI observations in the L, M, and N bands to probe the inner few AU of the RY Tau protoplanetary disk. A 2D temperature-gradient fit estimates the inner disk orientation, but a subsequent 3D radiative-transfer analysis shows that hot dust along the line of sight, likely in an envelope or disk wind, is required to reproduce the interferometric signatures and the SED. Spatially resolved dust mineralogy reveals multiple silicate species with a depletion of amorphous grains near the star, while grains including large sizes and crystalline components become more prominent outward. The best-fitting 3D model comprises an accretion disk accompanied by an optically thin envelope, and accretion luminosity is negligible in the mid-infrared; this highlights the importance of 3D structure in interpreting mid-IR interferometry of transition disks and supports a scenario where hot LOS dust shapes the near-IR/MIR observables.

Abstract

The T-Tauri type young stellar object RY Tau exhibits a dust depleted inner cavity characteristic of a transition disk. We constrain the spatial distribution and mineralogy of dust in the RY Tau protoplanetary disk in the inner few astronomical units using spectrally resolved interferometric observations in the L, M, and N bands obtained with VLTI/MATISSE. Employing a 2D temperature gradient model we estimate the orientation of the inner disk finding no evidence of significant misalignment between the inner and outer disk of RY Tau. Successively, we analyze the chemical composition of silicates depending on spatial region in the disk and identify several silicate species commonly found in protoplanetary disks. Additionally, a depletion of amorphous dust grains toward the central protostar is observed. Monte Carlo radiative transfer simulations show that hot dust close to the protostar and in the line of sight to the observer, either in the uppermost disk layers of a strongly flared disk or in a dusty envelope, is necessary to model the observations. The shadow cast by a dense innermost disk midplane on the dust further out explains the observed closure phases in the L band and to some extent in the M band. However, the closure phases in the N band are underestimated by our model, hinting at an additional asymmetry in the flux density distribution not visible at shorter wavelengths.

Figures (23)

• Figure 1: Overview of the MATISSE observations of RY Tau listed in Table \ref{['tab:observations']}. The corresponding $u$-$v$ coordinates are shown in Fig. \ref{['fig:u-v-coverage']}. Left panel: Squared visibilities $V^2$ over projected baseline length $B_\text{p}$ (pink/red: 813 wavelengths; blue/green: 3.55.2 wavelengths; see color bars). Middle panel: Measured closure phases $\phi_\text{cp}$ over the longest projected baseline length in the telescope triplet $B_\text{p;max}$. Right panel: Correlated fluxes $F_\text{corr}$ and corresponding projected baseline length $B_\text{p}$ and orientation $\phi_\text{B}$ in the $N$ band.
• Figure 2: Top row: Measured total flux $F_\text{tot}$. Bottom row: Derived disk-to-star flux ratio $f_\circ$ assuming stellar properties given in Table \ref{['tab:stellar_properties']} and wavelength binning as described in Sect. \ref{['sec:observations']}.
• Figure 3: Best fit of the temperature gradient model with the dust sublimation temperature $T_\text{in}$ as free parameter.
• Figure 4: Baselines of the MATISSE observations described in Sect. \ref{['sec:observations']}. The dashed line indicates the position angle of the disk major axis in the image plane.
• Figure 5: Wavelength-dependent mass absorption opacities derived from complex refractive index measurements for the dust species given in Table \ref{['tab:optical_data']}. Left column: Opacities derived assuming spherical compact grains. Right column: Opacities derived with the DHS approach assuming $f_\text{max} = 0.7$ for the amorphous silicates and graphite and $f_\text{max} = 0.99$ for the crystalline silicates.