Radial Variations in Grain Sizes and Dust Scale Heights in the Protoplanetary Disk around HD 163296 Revealed by ALMA Polarization Observations
Radial Variations in Grain Sizes and Dust Scale Heights in the Protoplanetary Disk around HD 163296 Revealed by ALMA Polarization Observations
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DOI：
10.3847/1538-4357/ab5107
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发表时间：
2019-10
期刊：
影响因子：
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通讯作者：
S. Ohashi;A. Kataoka
中科院分区：
文献类型：
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作者：
S. Ohashi;A. Kataoka
HD 163296的圆盘显示了阿塔卡玛大型毫米/亚毫米阵列观测到的环和间隙子结构。此外，这是唯一一个在毫米波偏振测量中空间分辨环和间隙的圆盘。在本文中，我们进行辐射传输模型，包括自散射偏振约束晶粒尺寸及其分布。我们发现，颗粒大小和尘埃尺度的高度是再现所观察到的偏振签名的径向和方位角分布的关键参数。径向变化主要由粒度决定。如果颗粒尺寸为λ/2π，则极化分数高;如果颗粒尺寸大于或小于该值，则极化分数低。相反，如果尘埃尺度高度增加，偏振的方位角变化会增强。基于对HD 163296偏振的详细建模，我们发现了以下颗粒尺寸和尘埃尺度高度的径向变化。最大晶粒尺寸为140 μm的间隙和显着更大或更小的环。70 Au环内的尘埃刻度高度小于气体刻度高度的三分之一，环外的尘埃刻度高度为气体刻度高度的三分之二。此外，我们将气体湍流在50 Au带隙中限制为α = 1.5 × 10−3，在90 Au带隙中限制为α = 0.015-0.3。在70 Au环边界处湍流强度的转变表明死区的存在。
The disk of HD 163296 shows ring and gap substructures in observations with the Atacama Large Millimeter/submillimeter Array. In addition, this is the only disk where the rings and gaps are spatially resolved in millimeter-wave polarization measurements. In this paper, we conduct radiative transfer modeling that includes self-scattering polarization to constrain the grain size and its distribution. We found that the grain size and dust scale height are the key parameters for reproducing the radial and azimuthal distributions of the observed polarization signature. Radial variation is mainly determined by grain size. The polarization fraction is high if the particle size is ∼λ/2π; it is low if the particle size is larger or smaller than this. In contrast, azimuthal variation in polarization is enhanced if the dust scale height is increased. Based on detailed modeling of the polarization of HD 163296, we found the following radial variations in the grain size and dust scale height. The maximum grain size was 140 μm in the gaps and significantly larger or smaller in the rings. The dust scale height is less than one-third of the gas scale height inside the 70 au ring, and two-thirds of it outside. Furthermore, we constrained the gas turbulence to be α ≲ 1.5 × 10−3 in the 50 au gap and α ∼ 0.015–0.3 in the 90 au gap. The transition in the turbulence strength at the boundary of the 70 au ring indicates the existence of a dead zone.