Oral Presentation
Constraining the dust size distribution in the protoplanetary disk around HD 163296 from the observed wavelength dependency of the dust ring width
Presenter: Kiyoaki Doi (NAOJ)
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 another indirect 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 analyzed high-resolution Band 4 (2.1 mm) and Band 6 (1.3 mm) images of the HD 163296 disk and found that the widths of the inner dust ring are similar at both wavelengths, but the outer dust ring is 1.2 times narrower in Band 4 than in Band 6. By comparing with simple dust ring models assuming size-dependent dust trapping, we constrained the dust size distribution, such as maximum dust size and dust size power law. We found that the maximum dust size is larger than 3 mm and the dust size power-law is steeper than 3.5 in the outer ring, while the maximum dust size is less than 500 um in the inner ring. These results suggest that the dust growth and possibly planetesimal formation are suppressed locally around the inner ring.
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