We use a kernel density estimator method to evaluate the stellar velocity dispersion in the open cluster NGC 2571. We derive the 3D velocity dispersion using both proper motions as extracted from Gaia Data Release 3 and single-epoch radial velocities as obtained with the instrument FLAMES at ESO's Very Large Telescope. The mean-square velocity along the line of sight is found to be larger than the one in the tangential direction by a factor of 6–8. We argue that the most likely explanation for such an occurrence is the presence of a significant quantity of unresolved binary and multiple stars in the radial velocity sample. Special attention should be paid to single-line spectroscopic binaries (SB1) since in this case we observe the spectral lines of the primary component only, and therefore the derived radial velocity is not the velocity of the binary system center of mass. To investigate this scenario, we performed numerical experiments varying the fractional abundance of SB1 in the observed sample. These experiments show that the increase of the mean-square radial velocity depends on the fractional abundance of SB1 to a power in the range [0.39, 0.45]. We used the 3D velocity dispersion obtained by the dispersions in the tangential directions and the assumption that the radial velocity dispersion is the same as a tangential one to estimate the virial cluster mass and the cluster mass, taking into account the gravitational field of the Galaxy and the nonstationarity of the cluster. These estimates are 650 ± 30 M _⊙ and 310 ± 80 M _⊙, respectively, in substantial agreement with the photometric cluster mass.

中文翻译：

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疏散星团 NGC 2571 的径向速度和自行运动的速度色散

我们使用核密度估计器方法来评估疏散星团 NGC 2571 中的恒星速度色散。我们使用从盖亚数据版本 3 中提取的自行以及使用 FLAMES 仪器在ESO 的甚大望远镜。沿视线方向的均方速度比切线方向的均方速度大 6-8 倍。我们认为，对这种现象最可能的解释是在视向速度样本中存在大量未解析的双星和多星。应特别注意单线光谱双星（SB1），因为在这种情况下我们仅观察到主要成分的光谱线，因此导出的径向速度不是双星系统质心的速度。为了研究这种情况，我们进行了改变观察样本中 SB1 丰度分数的数值实验。这些实验表明，均方径向速度的增加取决于 SB1 的分数丰度，其幂范围为 [0.39, 0.45]。我们使用由切向方向色散获得的 3D 速度色散以及径向速度色散与切向速度色散相同的假设来估计维里星团质量和星团质量，同时考虑到银河系的引力场和集群的非平稳性。这些估计值是 650 ± 30中号 _⊙和 310 ± 80中号 _⊙分别与光度团簇质量基本一致。