Keywords:HD 142527, protoplanetary disk, gas-to-dust ratio
We present the ALMA observations of the 98.5 GHz dust continuum and the 13CO J = 1 – 0 and C18O J = 1 – 0 line emission towards the protoplanetary disk of HD 142527. The 98.5 GHz continuum shows a strong azimuthal-asymmetric distribution similar to the previously reported 336 GHz continuum, and its peak emission at the dust concentrated northern region is optically thin at approximately 8 K. In every position angle, the peak brightness temperature of C18O J = 1 – 0 emission (≦ 25 K) is lower than that of the optically thick 13CO J = 3 – 2 (≈ 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 the ALMA Band 3 and Band 7 observations. In the analyses we assume the local thermodynamic equilibrium and the disk temperature to be the same as the peak brightness temperature of 13CO J = 3 – 2 with continuum emission. We successfully derived the gas-to-dust ratio G/D, defined as Σg/Σd, distribution across the disk. The ratio varies azimuthally, where it is ∼3 and ∼20 in the disk northern and southern regions, respectively. We also found that Σg varies approximately as ∝ Σd0.5, or equivalently G/D ∝ Σd-0.5. In addition, our results show that the peak Σd is located ahead of the peak Σg; if the latter correspond to a vortex of high gas pressure, the results indicate that the dust are trapped ahead of the vortex, which is predicted by theoretical studies.