Solving Grain Size Inconsistency between ALMA Polarization and VLA Continuum in the Ophiuchus IRS 48 Protoplanetary Disk
Solving Grain Size Inconsistency between ALMA Polarization and VLA Continuum in the Ophiuchus IRS 48 Protoplanetary Disk
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DOI：
10.3847/1538-4357/abaab4
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发表时间：
2020-07
期刊：
影响因子：
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通讯作者：
S. Ohashi;A. Kataoka;N. van der Marel;C. Hull;W. Dent;A. Pohl;P. Pinilla;E. V. van Dishoeck
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文献类型：
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作者：
S. Ohashi;A. Kataoka;N. van der Marel;C. Hull;W. Dent;A. Pohl;P. Pinilla;E. V. van Dishoeck
蛇夫座IRS 48周围的原行星盘在（亚）毫米观测中显示出方位不对称的尘埃分布，这被解释为一个漩涡，毫米/厘米大小的粒子被困在连续峰的位置。本文介绍了860 μm的阿尔马观测资料。偏振发射被检测到朝向盘的一部分。偏振矢量平行于光盘短轴，并推导出偏振分数为1%-2%。这些特征与亚毫米波辐射的自散射模型一致，表明最大晶粒尺寸为100 μm。然而，这与先前对毫米/厘米尘埃颗粒被漩涡捕获的解释不一致。为了解释阿尔马偏振和以前的阿尔马和甚大阵观测，我们认为，在860 μm波长的热发射是光学厚（τabs <$7.3）的尘埃陷阱，最大可观察到的颗粒大小为100 μm，而不是光学薄的情况下，厘米大小的尘埃颗粒。我们注意到，如果860 μm的热辐射是光学厚度的，我们不能排除更大的尘埃颗粒聚集在中平面附近。
The protoplanetary disk around Ophiuchus IRS 48 shows an azimuthally asymmetric dust distribution in (sub)millimeter observations, which is interpreted as a vortex, where millimeter/centimeter-sized particles are trapped at the location of the continuum peak. In this paper, we present 860 μm ALMA observations of polarized dust emission from this disk. The polarized emission was detected toward a part of the disk. The polarization vectors are parallel to the disk minor axis, and the polarization fraction was derived to be 1%–2%. These characteristics are consistent with models of self-scattering of submillimeter-wave emission, which indicate a maximum grain size of ∼100 μm. However, this is inconsistent with the previous interpretation of millimeter/centimeter dust particles being trapped by a vortex. To explain both ALMA polarization and previous ALMA and Very Large Array observations, we suggest that the thermal emission at 860 μm wavelength is optically thick (τabs ∼ 7.3) at the dust trap with a maximum observable grain size of ∼100 μm rather than an optically thin case with centimeter-sized dust grains. We note that we cannot rule out that larger dust grains are accumulated near the midplane if the 860 μm thermal emission is optically thick.