We constructed a Hubble Space Telescope (HST) astro-photometric catalog of the central region of the Galactic globular cluster NGC 1261. This catalog, complemented with Gaia DR2 data sampling the external regions, has been used to estimate the structural parameters of the system (i.e., core, half-mass, tidal radii and concentration) from its resolved star density profile. We computed high-precision proper motions thanks to multi-epoch HST data and derived the cluster velocity dispersion profile in the plane of the sky for the innermost region, finding that the system is isotropic. The combination with line-of-sight information collected from spectroscopy in the external regions provided us with the cluster velocity dispersion profile along the entire radial extension. We also measured the absolute proper motion of NGC 1261 using a few background galaxies as a reference. The radial distribution of the Blue Straggler Star population shows that the cluster is in a low/intermediate phase of dynamical evolution.

中文翻译：

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NGC 1261 的运动学视图：结构参数、内部色散、绝对正确运动和蓝色落后星

我们构建了星系球状星团 NGC 1261 中心区域的哈勃太空望远镜 (HST) 天文光度目录。该目录与对外部区域采样的 Gaia DR2 数据相辅相成，已被用于估计系统的结构参数（即核心、半质量、潮汐半径和浓度）来自其解析的恒星密度剖面。由于多历元 HST 数据，我们计算了高精度的自行，并导出了最内部区域在天空平面中的星团速度色散剖面，发现系统是各向同性的。与从外部区域的光谱收集的视线信息相结合，为我们提供了沿整个径向延伸的星团速度色散剖面。我们还使用一些背景星系作为参考测量了 NGC 1261 的绝对自行运动。Blue Straggler Star 种群的径向分布表明该星团处于动力学演化的低/中阶段。