Turbulence is a crucial factor in many models of planet formation, but it has only been directly constrained among a small number of planet forming disks. Building on the upper limits on turbulence placed in disks around HD 163296 and TW Hya, we present ALMA CO J=2-1 line observations at $\sim0.3"$ (20-50 au) resolution and 80 ms$^{-1}$ channel spacing of the disks around DM Tau, MWC 480, and V4046 Sgr. Using parametric models of disk structure, we robustly detect non-thermal gas motions around DM Tau of between 0.25 c$_s$ and 0.33 c$_s$, with the range dominated by systematic effects, making this one of the only systems with directly measured non-zero turbulence. Using the same methodology, we place stringent upper limits on the non-thermal gas motion around MWC 480 ($<$0.08c$_s$) and V4046 Sgr ($<$0.12 c$_s$). The preponderance of upper limits in this small sample, and the modest turbulence levels consistent with dust studies, suggest that weak turbulence ($\alpha\lesssim10^{-3}$) may be a common, albeit not universal, feature of planet-forming disks. We explore the particular physical conditions around DM Tau that could lead this system to be more turbulent than the others.

中文翻译：

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使用 ALMA 测量行星形成盘中的湍流运动：DM Tau 周围的检测和 MWC 480 和 V4046 Sgr 周围的未检测

湍流是许多行星形成模型中的一个关键因素，但它只被直接限制在少数行星形成盘中。基于 HD 163296 和 TW Hya 周围盘中湍流的上限，我们在 $\sim0.3"$ (20-50 au) 分辨率和 80 ms$^{- 1}DM Tau、MWC 480 和 V4046 Sgr 周围圆盘的通道间距。使用圆盘结构的参数模型，我们稳健地检测到 DM Tau 周围 0.25 c$_s$ 和 0.33 c$_s$ 之间的非热气体运动, 范围以系统效应为主，使其成为仅有的直接测量非零湍流的系统之一。使用相同的方法，我们对 MWC 480 附近的非热气体运动设置了严格的上限 ($<$0.08c$ _s$) 和 V4046 Sgr ($<$0.12 c$_s$)。在这个小样本中上限的优势，以及与尘埃研究一致的适度湍流水平，表明弱湍流（$\alpha\lesssim10^{-3}$）可能是行星的一个常见的，尽管不是普遍的特征——形成磁盘。我们探索了 DM Tau 周围的特殊物理条件，这些条件可能导致该系统比其他系统更加动荡。