午餐會報 (2023)

Planet formation begins with the coagulation of dust grains in protoplanetary disks. Therefore, constraints on the dust size distribution in the disks can provide a clue to understanding planet formation. Previous studies have estimated the dust size distribution using the spectral index derived from multi-wavelength observations or dust polarization observations. However, these studies give different results depending on their methods and model assumptions 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. In many disks, there are dust and gas rings, and larger dust grains are more effectively trapped in the gas rings, forming narrower dust rings. As a result, the dust rings are expected to appear narrower at longer wavelengths since the observations are sensitive to the dust grains whose size is comparable to the observed wavelength. We analyze high-resolution Band 4 (2.1 mm) and Band 6 (1.3 mm) images of the HD 163296 disk. We find for the first time that the width of the outer dust ring (100 au) appears 1.2 times narrower at the longer wavelength, while the width of the inner ring (67 au) is similar between the two bands. The difference in the ring width depending on the observed wavelength is consistent with the dust trapping scenario in a gas ring. We constrain the maximum dust size a_max and the exponent of the dust size distribution p from the difference in dust ring width between the two bands, together with the spectral index, and found that 1 mm < a_max < 20 mm and p < 3.5 in the inner ring, and a_max > 30 mm and 3.4 < p < 3.6 in the outer ring. These results suggest that the degree of dust growth is spatially dependent, which could affect the formation of planetesimals.

Protostellar jets are the most intriguing characteristics in the magnetized, accreting young stellar objects. The ejection of jets and accretion outbursts are closely related to the formation of complex organic molecules (COMs) in the class 0/I protostars. However, the launching mechanism of the protostellar jet and its correlation with COMs formation are not constrained observationally. In this presentation, I shall briefly introduce the current theory of jet launching. Then I shall present our recent results on jet/outflow from the high spatial resolution and high sensitivity observations with Atacama Large Millimeter/submillimeter Array (ALMA), which is currently the largest radio interferometry array on Earth. Finally, I shall describe the possible connection of the jet with the accretion burst and formation of complex organic molecules within the disk, which would be the chemical composition of future planets.