Significant gas-to-dust ratio asymmetry and variation in the disk of HD 142527 and the indication of gas depletion

Abstract

We investigate the dust and gas distribution in the disk around HD 142527 based on ALMA observations of dust continuum emissions, 13CO J = 3-2 and C18O J = 3-2. The disk shows strong azimuthal asymmetry in the dust continuum emission, while gas emission is more symmetric. In this paper, we investigate how gas and dust are distributed in the dust-bright northern part of the disk and in the dust-faint southern part. We construct two axisymmetric disk models. One reproduces the radial profiles of the continuum and the velocity moments 0 and 1 of CO lines in the north, and the other reproduces those in the south. We have found that the dust is concentrated in a narrow ring of ∼50 au width (in FWHM; wd = 30 au in our parameter definition), located at ∼170-200 au from the central star. The dust particles are strongly concentrated in the north. We have found that the dust surface density contrast between the north and the south amounts to ∼70. Compared to the dust, the gas distribution is more extended in the radial direction. We find that the gas component extends at least from ∼100 au to ∼250 au from the central star, and there should also be tenuous gas remaining inside and outside of these radii. The azimuthal asymmetry of gas distribution is much smaller than dust. The gas surface density differs only by a factor of ∼3-10 between the north and south. Hence, the gas-to-dust ratio strongly depends on the location of the disk: ∼30 at the location of the peak of dust distribution in the south and ∼3 at the location of the peak of dust distribution in the north. Despite large uncertainties, we infer that the overall gas-to-dust ratio is ∼10-30, indicating that the gas depletion may already have been under way.