Constraints on the dust size distributions in the HD 163296 disk from the difference of the apparent dust ring widths between two ALMA Bands
Speaker: Kiyoaki Doi
Abstract :
The formation of planets begins with dust coagulation in protoplanetary disks. Therefore, constraints on the dust size distribution in the disks can be a clue for understanding planet formation. In previous studies, the dust size has been estimated by using the spectral index derived from multi-wavelength observations or dust polarization observations. However, these studies provide different results depending on their methods and models and do not reach a consensus.
In this work, we propose a new method to constrain the dust size distribution by using the wavelength dependency of the dust ring widths. Since larger dust grains are trapped more effectively in the gas pressure bump, they form narrower rings. As a result, the dust rings appear narrower at longer wavelength observations since observations are sensitive to the dust grains whose size is comparable to the observed wavelength.
We constrain the dust size distribution in the HD 163296 disk using ALMA high-resolution observations in Band 6 (1.25 mm) and Band 4 (2.14 mm). We focus on the two clear dust rings in the disk and find that the outer ring at 100 au appears narrower at the longer wavelength, while the inner ring at 67 au appears similar between the two bands. We model a dust ring assuming size-dependent dust trapping at a gas pressure maxima and investigate the relation between the wavelength dependency of the ring width and the spectral index, and the dust size distribution. By comparing the model with the observations, we constrain the maximum dust size a_max and the exponent of the power law dust size distribution p. We constrain that 0.9 mm < a_max < 5 mm and p < 3.3 in the inner ring, and 35 mm < a_max > 1000 mm and 3.4 < p < 3.7 in the outer ring. The larger maximum dust size in the outer ring suggests that the degree of dust growth is spatially dependent, which could affect the location of the planetesimal formation.