EWOCS-VIII：基于VVVX自行的Westerlund 1内部运动学与膨胀特性
EWOCS-VIII: Internal kinematics and expansion of Westerlund 1 from VVVX proper motions
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中文总结 AI 辅助
该研究利用VVVX自行数据，分析Westerlund 1的内部运动学，发现其外区显著膨胀、中心区或存在质量分层，结果支持近乎整体形成的情景。
中文摘要 AI 辅助
Westerlund 1（Wd1）是银河系中已知质量最大的年轻星团，是研究大质量星团早期动力学演化的关键实验室。由于其消光程度较高，其中等质量恒星族的内部运动学仍在很大程度上未被探索。我们旨在通过对近红外（NIR）选择的星团成员及其自行（PM）进行均匀普查，来表征Wd1的内部运动学特性。我们采用了基于多历元VVV/VVVX观测的VIRAC2星表中的自行数据。对于此前通过NIR测光和天体测量（Paper I）确定的1286个候选成员，我们计算了它们相对于星团平均运动的自行，并根据位置和半径对其进行了分析。我们还研究了径向趋势，测试了结果对假设星团中心的稳健性，并搜索了运动的偏好方向。我们检测到Wd1外区域存在统计上显著的膨胀信号，相对自行的径向分量随与星团中心距离的增加而增大。膨胀呈现不对称性，在天空平面内沿方位角PA=84°±8°方向检测到最强梯度，显著性达5.9σ。我们还发现中心区域存在向内径向运动的迹象，这与正在进行的质量分层一致，但显著性仅约为2σ。综合来看，这些结果与近乎整体形成的情景相符。
英文摘要
Westerlund 1 (Wd1) is the most massive young star cluster known in the Milky Way and a key laboratory for studying the early dynamical evolution of massive clusters. Owing to its high extinction, the internal kinematics of its intermediate-mass stellar population remain largely unexplored. We aim to characterize the internal kinematic properties of Wd1 using a homogeneous census of near-infrared (NIR) selected cluster members and their proper motions (PMs). We considered PMs from the VIRAC2 catalog, based on multi-epoch VVV/VVVX observations. For $1286$ candidate members previously identified through NIR photometry and astrometry (Paper I), we computed their PMs relative to the cluster mean motion and analyzed them as a function of position and radius. We also investigate radial trends, test the robustness of the results against the assumed cluster center, and search for preferred directions of motion. We detect a statistically significant signature of expansion in the outer regions of Wd1, with the radial component of the relative PMs increasing with distance from the cluster center. The expansion appears asymmetric, with the strongest gradient detected along a PA$=84\degree \pm 8\degree$ in the plane of the sky and with $5.9σ$ significance. We also find hints for inward radial motions in the central region, consistent with ongoing mass segregation, but only at $\approx 2σ$ significance. Taken together, these results are consistent with a nearly monolithic formation scenario.
