We present a study, based on Gaia DR2, of the population of blue straggler stars (BSS) in the open clusters Trumpler 5, Trumpler 20, and NGC 2477. All candidates were selected according to their position in the color-magnitude diagram, to their proper motion components, and to their parallax. We also looked for yellow stragglers, i.e., possible evolved blue stragglers. We found that Trumpler 5 hosts a large BSS population, which allowed us to analyze their radial distribution as a probe of the cluster's dynamical status. The BSS distribution was compared with that of red giant branch stars (RGB) to evaluate mass segregation. Our results indicate that blue straggler stars are not more centrally concentrated than RGB stars in any of the clusters. The radial distribution of BSS in Trumpler 5 is flat. Additionally, using a multi-epoch radial velocity survey conducted with the high-resolution spectrograph FLAMES/GIRAFFE at VLT, we measured the radial velocities of a sample of stragglers, for the sake of comparison with the mean radial velocity and the velocity dispersion of the clusters. Based on the radial velocity variations for different epochs, we roughly classified these stars as possible close-or long-period binaries.

中文翻译：

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疏散星团 Trumpler 5、Trumpler 20 和 NGC 2477 的蓝色落后种群

我们基于 Gaia DR2 对疏散星团 Trumpler 5、Trumpler 20 和 NGC 2477 中的蓝色落后星 (BSS) 进行了一项研究。它们的自行分量，以及它们的视差。我们还寻找黄色掉队者，即可能进化的蓝色掉队者。我们发现 Trumpler 5 拥有大量 BSS 种群，这使我们能够分析它们的径向分布，作为对集群动态状态的探测。将 BSS 分布与红巨星分支星 (RGB) 的分布进行比较以评估质量偏析。我们的结果表明，在任何一个星团中，蓝色落后星并不比 RGB 星更集中。Trumpler 5 中 BSS 的径向分布是平坦的。此外，使用高分辨率光谱仪 FLAMES/GIRAFFE 在 VLT 进行的多历元径向速度调查，我们测量了散兵游勇样本的径向速度，以便与平均径向速度和星团的速度色散进行比较。根据不同时期的径向速度变化，我们粗略地将这些恒星归类为可能的近周期或长周期双星。