An Observational Study for Grain Dynamics in the AS 209 Disk with Submillimeter Polarization
An Observational Study for Grain Dynamics in the AS 209 Disk with Submillimeter Polarization
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DOI：
10.3847/1538-4357/ab3575
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发表时间：
2019-07
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影响因子：
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通讯作者：
Tomohiro Mori;A. Kataoka;S. Ohashi;M. Momose;T. Muto;H. Nagai;T. Tsukagoshi
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作者：
Tomohiro Mori;A. Kataoka;S. Ohashi;M. Momose;T. Muto;H. Nagai;T. Tsukagoshi
我们对 AS 209 周围的 II 类原行星盘进行了 870 μm 阿塔卡马大型毫米波阵列偏振观测，该盘具有同心、多个间隙和环。我们成功地检测到偏振发射，并发现内部和外部区域的偏振方向和分数具有不同的特征。在内部区域，偏振方向平行于圆盘的短轴，这与自散射模型一致。该区域的平均极化率约为 0.2%，低于晶粒具有最大极化效率时的预期值，对应于晶粒半径 λ/2π ∼ 140 μm。在外部区域，我们检测到〜1.0％的偏振并发现偏振方向几乎在方位角方向。此外，偏振方向与方位角方向有系统的角度偏差，Δθ ∼ 4.°5 ± 1.°6。该模式与其中径向漂移的尘埃颗粒通过气流与尘埃颗粒对齐的模型一致。我们考虑了 AS 209 环上颗粒动力学的可能情况，可以重现偏振图案。然而，观察到的角度偏差的方向与基于圆盘顺时针旋转的事实预测的方向相反。这提出了一个关于我们对原行星盘中的排列过程和/或颗粒动力学的理解的问题。
We present an 870 μm Atacama Large Millimeter Array polarization observation toward the Class II protoplanetary disk around AS 209, which has concentric, multiple gaps and rings. We successfully detect the polarized emission and find that the polarization orientations and fractions have distinct characteristics between the inner and outer regions. In the inner region, the polarization orientations are parallel to the minor axis of the disk, which is consistent with the self-scattering model. The mean polarization fraction in the region is ∼0.2%, which is lower than the expected value when the grains have the maximum polarization efficiency, which corresponds to λ/2π ∼ 140 μm in grain radius. In the outer region, we detect ∼1.0% polarization and find that the polarization orientations are almost in the azimuthal directions. Moreover, the polarization orientations have systematic angular deviations from the azimuthal directions with Δθ ∼ 4.°5 ± 1.°6. The pattern is consistent with a model in which radially drifting dust grains are aligned by the gas flow against the dust grains. We consider possible scenarios of the grain dynamics at the AS 209 ring that can reproduce the polarization pattern. However, the directions of the observed angular deviations are opposite to what is predicted based on the fact that the disk rotates clockwise. This raises a question regarding our understanding of the alignment processes and/or grain dynamics in protoplanetary disks.