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

We present ALMA observations of the 98.5 GHz dust continuum and the 13CO J = 1 − 0 and C18O J = 1 − 0 line emissions of the protoplanetary disk associated with HD 142527. The 98.5 GHz continuum reveals a strong azimuthal-asymmetric distribution similar to that of the previously reported 336 GHz continuum, with a peak emission in dust concentrated region in the north. The peak brightness temperature is approximately 8 K, indicating that the emission is optically thin. At every position angle, the peak brightness temperature of the C18O J =1−0 emission (less than 25 K) is lower than that of the optically thick 13CO J = 3 − 2 (about 36 K), indicating that the C18O is optically thin. We derive the gas and dust surface densities, Σg and Σd, of the disk of HD 142527 by using ALMA Band 3 and Band 7 observations. In the analyses, we assume the local thermodynamic equilibrium and the disk temperature to be equal to the peak brightness temperature of 13CO J = 3 − 2 with a continuum emission. We successfully derived the gas-to-dust ratio G/D, defined as Σg/Σd, distributed across the disk. The ratio varies azimuthally, where it is about 3 and 20 in the northern and southern regions of the disk, respectively. We also found that Σg varies proportional to Σd with a power law of exponent 0.47, or equivalently G/D is proportional to Σd with a power law of exponent –0.53. In addition, our results show that the peak Σd is located ahead of the peak Σg; if the latter corresponds to a vortex of high gas pressure, the results indicate that the dust is trapped ahead of the vortex, which is as predicted by theoretical studies.