Investigating the gas-to-dust ratio in the protoplanetary disk of HD 142527

TL;DR

This study uses ALMA observations to analyze the distribution of gas and dust in the HD 142527 protoplanetary disk, revealing azimuthal variations in the gas-to-dust ratio and dust grain sizes, supporting dust trapping theories.

Contribution

First detailed mapping of gas and dust surface densities and their ratio variations in HD 142527, linking dust trapping to high-pressure regions in the disk.

Findings

Gas-to-dust ratio varies azimuthally as G/D ∝ Σ_d^(-0.53)

Dust spectral index β differs between northern and southern regions

Peak dust surface density is located ahead of the gas peak, indicating dust trapping

Abstract

We present ALMA observations of the $98.5~\mathrm{GHz}$ dust continuum and the $\mathrm{^{13}CO}~J = 1 - 0$ and $\mathrm{C^{18}O}~J = 1 - 0$ line emissions of the protoplanetary disk associated with HD~142527. The $98.5~\mathrm{GHz}$ continuum shows a strong azimuthal-asymmetric distribution similar to that of the previously reported $336~\mathrm{GHz}$ continuum, with a peak emission in dust concentrated region in the north. The disk is optically thin in both the $98.5~\mathrm{GHz}$ dust continuum and the $\mathrm{C^{18}O}~J = 1 - 0$ emissions. We derive the distributions of gas and dust surface densities, $\Sigma_\mathrm{g}$ and $\Sigma_\mathrm{d}$, and the dust spectral opacity index, $\beta$, in the disk from ALMA Band 3 and Band 7 data. In the analyses, we assume the local thermodynamic equilibrium and the disk temperature to be equal to the peak brightness temperature of $\mathrm{^{13}CO}~J = 3 - 2$ with a continuum emission. The gas-to-dust ratio, $\mathrm{G/D}$, varies azimuthally with a relation $\mathrm{G/D} \propto \Sigma_\mathrm{d}^{-0.53}$, and $\beta$ is derived to be $\approx 1$ and $\approx 1.7$ in the northern and southern regions of the disk, respectively. These results are consistent with the accumulation of larger dust grains in a higher pressure region. In addition, our results show that the peak $\Sigma_\mathrm{d}$ is located ahead of the peak $\Sigma_\mathrm{g}$. If the latter corresponds to a vortex of high gas pressure, the results indicate that the dust is trapped ahead of the vortex, as predicted by some theoretical studies.