Title: On the degree of stochastic asymmetry in the tidal tails of star clusters Show Chinese title

Title: 星团潮汐尾的随机不对称性的程度

Abstract: Context: Tidal tails of star clusters are commonly understood to be populated symmetrically. Recently, the analysis of Gaia data revealed large asymmetries between the leading and trailing tidal tail arms of the four open star clusters Hyades, Praesepe, Coma Berenices and NGC 752. Aims: As the evaporation of stars from star clusters into the tidal tails is a stochastic process, the degree of stochastic asymmetry is quantified in this work. Methods: For each star cluster 1000 configurations of test particles are integrated in the combined potential of a Plummer sphere and the Galactic tidal field over the life time of the particular star cluster. For each of the four star clusters the distribution function of the stochastic asymmetry is determined and compared with the observed asymmetry. Results: The probabilities for a stochastic origin of the observed asymmetry of the four star clusters are: Praesepe ~1.7 sigma, Coma Berenices ~2.4 sigma, Hyades ~6.7 sigma, NGC 752 ~1.6 sigma. Conclusions: In the case of Praesepe, Coma Berenices and NGC 752 the observed asymmetry can be interpreted as a stochastic evaporation event. However, for the formation of the asymmetric tidal tails of the Hyades additional dynamical processes beyond a pure statistical evaporation effect are required. Show Chinese abstract

Abstract: 上下文：星团的潮汐尾通常被认为是对称分布的。最近，对盖亚数据的分析揭示了四个开放星团——Hyades、Praesepe、Coma Berenices 和 NGC 752 的前导和后随潮汐尾臂之间存在大的不对称性。目标：由于恒星从星团蒸发进入潮汐尾是一个随机过程，本文量化了随机不对称性的程度。方法：对于每个星团，在普尔默球和银河潮汐场的联合势场中，对1000个测试粒子的配置进行积分，持续时间与特定星团的寿命相同。对于四个星团中的每一个，确定随机不对称性的分布函数，并与观测到的不对称性进行比较。结果：四个星团观测到的不对称性随机起源的概率分别为：Praesepe 约 1.7 sigma，Coma Berenices 约 2.4 sigma，Hyades 约 6.7 sigma，NGC 752 约 1.6 sigma。结论：在 Praesepe、Coma Berenices 和 NGC 752 的情况下，观测到的不对称性可以解释为随机蒸发事件。然而，对于 Hyades 不对称潮汐尾的形成，除了纯粹的统计蒸发效应外，还需要额外的动力学过程。