The Hercules ultrafaint dwarf galaxy (UFD) has long been hypothesized to be tidally disrupting, yet no conclusive evidence has been found for tidal disruption owing partly to difficulties in identifying Hercules member stars. In this work, we present a homogeneous reanalysis of new and existing observations of Hercules, including the detection of a new potential member star located ∼1° (∼1.7 kpc) west of the center of the system. In addition to measuring the line-of-sight velocity gradient, we compare predictions from dynamical models of stream formation to these observations. We report an updated velocity dispersion measurement based on 28 stars, 1.9−0.6+0.6 km s⁻¹, which is significantly lower than previous measurements. We find that the line-of-sight velocity gradient is 1.8−1.8+1.8 km s⁻¹ kpc along the major axis of Hercules, consistent with zero within 1σ. Our dynamical models of stream formation, on the other hand, can reproduce the morphology of the Hercules UFD, specifically the misalignment between the elongation and the orbital motion direction. Additionally, these dynamical models indicate that any radial velocity gradient from tidal disruption would be too small, 0.00−0.91+0.97 km s⁻¹ kpc, to be detectable with current sample sizes. Combined with our analysis of the tidal radius evolution of the system as a function of its orbital phase, we argue that it is likely that Hercules is indeed currently undergoing tidal disruption in its extended stellar halo with a line-of-sight velocity gradient too small to be detected with current observational data sets.

中文翻译：

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武仙超微弱矮星系潮汐扰动的特征* * 本文包含使用位于智利拉斯坎帕纳斯天文台的 6.5 m 麦哲伦望远镜收集的数据。

大力神超微弱矮星系（UFD）长期以来一直被假设具有潮汐扰乱，但由于难以识别大力神成员恒星，因此尚未发现潮汐扰乱确实证据。在这项工作中，我们对武仙座的新观测和现有观测进行了均质再分析，包括检测到位于系统中心以西约 1°（约 1.7 kpc）处的新潜在成员星。除了测量视线速度梯度之外，我们还将溪流形成动力学模型的预测与这些观测结果进行比较。我们报告了基于 28 颗恒星的更新的速度色散测量， 1.9-0.6+0.6 km s ^-1，明显低于之前的测量值。我们发现视线速度梯度为 1.8-1.8+1.8 km s ⁻¹ kpc 沿大力神长轴，与 1 内的零一致σ。另一方面，我们的流形成动力学模型可以重现 Hercules UFD 的形态，特别是伸长和轨道运动方向之间的错位。此外，这些动力学模型表明潮汐破坏引起的任何径向速度梯度都太小， 0.00-0.91+0.97 km s ⁻¹ kpc，可使用当前样本量进行检测。结合我们对该系统的潮汐半径演化作为其轨道相位的函数的分析，我们认为大力神星目前可能确实在其扩展的恒星晕中经历潮汐破坏，而视线速度梯度太小可以用当前的观测数据集来检测。