Detailed modeling of dust distribution in the disk of HD 142527

Abstract

We investigate the dust distribution in the crescent disk around HD 142527 based on the continuum emission at 890 μm obtained by ALMA Cycle 0. The map is divided into 18 azimuthal sectors, and the radial intensity profile in each sector is reproduced with a two-dimensional disk model. Our model takes account of scattering and inclination of the disk as well as the azimuthal dependence in intensity. When the dust is assumed to have the conventional composition and a maximum size of 1 mm, the northwestern region (PA = 291°-351°) cannot be reproduced. This is because the model intensity becomes insensitive to the increase in surface density due to heavy self-scattering, reaching its ceiling much lower than the observed intensity. The ceiling depends on the position angle, PA. When the scattering opacity is reduced by a factor of 10, the intensity distribution is reproduced successfully in all the sectors, including those in the northwestern region. The best-fitting model parameters depend little on the scattering opacity in the southern region where the disk is optically thin. The contrast ratio of dust surface densities along PA is derived to be about 40, much smaller than the value in the case of conventional opacities (70-130). These results strongly suggest that the albedo is lower than that considered for some reason, at least in the northwestern region.