To study the dust dynamics in the dust-trapping vortices in the protoplanetary disk around MWC 758, we analyzed the 1.3 mm continuum images of the MWC 758 disk obtained with the Atacama Large Millimeter/submillimeter Array in 2017 and 2021. We detect proper motions of 22 mas and 24 mas in the two dust clumps at radii of 0.″32 and 0.″54 in the disk on the plane of the sky, respectively. On the assumption that the dust clumps are located in the disk midplane, the velocities of the observed proper motions along the azimuthal direction of the inner and outer dust clumps are sub- and super-Keplerian, respectively, and both have angular velocities corresponding to the Keplerian angular velocity at a radius of 0.″46 ± 0.″04. This deviation from the Keplerian motion is not expected in the conventional theory of vortices formed by the Rossby wave instability. The observed non-Keplerian proper motions of the dust clumps are unlikely due to the disk warp and eccentricity, nor are they associated with any predicted planets. The two dust clumps are likely spatially coincident with the infrared spirals. In addition, we detect the changes in the intensity profiles of the dust clumps over the 4 yr span. Therefore, we suggest that the observed proper motions are possibly due to changes in the density distributions in the dust clumps caused by their interaction with the spirals in the disk.

中文翻译：

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ALMA 对原行星盘中尘埃团块正常运动的观测 MWC 758


为了研究 MWC 758 周围原行星盘中吸尘涡旋中的尘埃动力学，我们分析了 2017 年和 2021 年使用阿塔卡马大型毫米/亚毫米阵列获得的 MWC 758 盘的 1.3 mm 连续图像。我们在天空平面上的圆盘中分别在半径为 0.“32 和 0.”54 的两个尘埃团中检测到 22 mas 和 24 mas 的正确运动。假设尘埃团位于圆盘中平面，则观察到的沿内外尘埃团的方位角方向的正确运动速度分别为亚开普勒和超开普勒，并且两者都具有对应于半径为 0.“46 ± 0.”04 的开普勒角速度的角速度。这种与开普勒运动的偏差在由 Rossby 波不稳定形成的漩涡的传统理论中是意料不到的。由于圆盘的翘曲和偏心率，观测到的尘埃团的非开普勒正常运动不太可能，它们也与任何预测的行星无关。这两个尘埃团在空间上可能与红外螺旋重合。此外，我们还检测了 4 年跨度内尘埃团强度分布的变化。因此，我们认为观察到的正确运动可能是由于尘埃团与盘中螺旋的相互作用引起的尘埃团密度分布的变化。