PDS 70外盘臂状结构分析。螺旋密度波还是漩涡？
Analysis of the arm-like structure in the outer disk of PDS 70. Spiral density wave or vortex?
摘要：
观察行星和盘之间的动力学相互作用是理解它们形成和演化的关键。最近在PDS 70的原行星盘内发现了两颗原行星，以及朝向恒星西北的臂状结构。我们的目标是限制这种臂状结构的形态和起源，并评估它是否可以追踪行星PDS 70 c和圆盘之间动力学相互作用引起的螺旋密度波。我们分析了偏振和角度差分成像（PDI和ADI）的数据与VLT/SPHERE，跨越六年的观测。PDI数据集使用IRDAP极化数据缩减管道进行缩减，而ADI数据集使用MUSTARD进行处理，MUSTARD是一种新颖的逆问题算法，用于解决破坏先前用于分析该磁盘的图像的几何偏差。我们确认了所有PDI和ADI数据集中臂状结构的存在。我们没有观察到一个东南对称的手臂相对于磁盘短轴，这似乎不赞成以前的假设，手臂是一个双环结构的足迹。如果该结构跟踪PDS 70 c运动后的螺旋密度波，我们预计螺旋的$11\overset{\circ}{.}28^{+2\overset{\circ}{.}20}_{-0\overset{\circ}{.}86}$旋转在六年内。然而，我们没有测量结构的任何显著移动。如果臂状结构是一个行星驱动的旋臂，观察到的旋转的缺乏将表明，刚体旋转的假设可能是不适当的行星诱导的螺旋。我们认为，臂状结构，而不是跟踪漩涡出现在一个单臂螺旋散射光由于投影效应。涡旋假说解释了观测到的旋转的缺乏和ALMA检测到的附近亚毫米连续不对称性的存在。
英文摘要：
Observing dynamical interactions between planets and disks is key to understanding their formation and evolution. Two protoplanets have recently been discovered within PDS 70's protoplanetary disk, along with an arm-like structure towards the north-west of the star. Our aim is to constrain the morphology and origin of this arm-like structure, and to assess whether it could trace a spiral density wave caused by the dynamical interaction between the planet PDS 70c and the disk. We analyze polarized and angular differential imaging (PDI and ADI) data taken with VLT/SPHERE, spanning six years of observations. PDI data sets are reduced using the IRDAP polarimetric data reduction pipeline, while ADI data sets are processed using MUSTARD, a novel inverse problem algorithm to tackle the geometrical biases spoiling the images previously used for the analysis of this disk. We confirm the presence of the arm-like structure in all PDI and ADI datasets. We do not observe a south-east symmetric arm with respect to the disk minor axis, which seems to disfavor the previous hypothesis that the arm is the footprint of a double-ring structure. If the structure traces a spiral density wave following the motion of PDS 70c, we would expect $11\overset{\circ}{.}28^{+2\overset{\circ}{.}20}_{-0\overset{\circ}{.}86}$ rotation for the spiral in six years. However, we do not measure any significant movement of the structure. If the arm-like structure is a planet-driven spiral arm, the observed lack of rotation would suggest that the assumption of rigid-body rotation may be inappropriate for spirals induced by planets. We suggest that the arm-like structure may rather trace a vortex appearing as a one-armed spiral in scattered light due to projection effects. The vortex hypothesis accounts for both the lack of observed rotation and the presence of a nearby sub-mm continuum asymmetry detected with ALMA.
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