标题： NGC 3603年轻星团的内部动力学和成员资格来自微角秒天文学 显示英文标题

标题： Internal dynamics and membership of the NGC 3603 Young Cluster from microarcsecond astrometry

摘要： 我们分析了来自哈勃空间望远镜宽视场行星相机2（HST/WFPC2）的两期观测数据，目的是研究NGC 3603年轻星团的动力学特性和恒星群体。通过对超过800颗恒星在10.15年时间跨度内的自行测量，我们能够区分出星团成员与场星。 最佳拟合等时线给出的消光值为Av=4.6-4.7 mag，距离为6.6-6.9 kpc，NGC 3603年轻星团（NYC）的年龄为1 Myr。 我们识别出了位于短暂存在的辐射对流间隙中的主序前阶段/主序过渡阶段恒星，该间隙在NYC中出现在质量范围为3.5至3.8倍太阳质量之间。 我们还识别出了一组稀疏分布的年龄约为4 Myr的恒星，这些恒星似乎是之前发现的位于巨大电离氢区NGC 3603中的蓝超巨星的低质量对应体。 首次，我们能够从亮度I<18.5 mag的234颗恒星中测量星爆星团内部的速度弥散度，得到的结果为{\sigma }_pm1D=141+/-27 {\mu }弧秒/年（在6.75千秒差距的距离上相当于4.5+/-0.8公里/秒）。 由于质量介于1.7到9倍太阳质量之间的所有恒星都表现出相同的速度弥散度，这意味着星团中的恒星尚未达到动能平衡（即星团未处于引力平衡状态）。 这些结果凸显了高精度天体测量和测光结合的强大作用，并强调了NYC作为测试恒星演化模型和年轻星团动力学模型的基准对象，以及作为星系外星团模板的重要性。 显示英文摘要

摘要： We have analyzed two epochs of HST/WFPC2 observations of the young Galactic starburst cluster in NGC 3603 with the aim to study its internal dynamics and stellar population. Relative proper motions measured over 10.15 yrs of more than 800 stars enable us to distinguish cluster members from field stars. The best-fitting isochrone yields Av=4.6-4.7 mag, a distance of 6.6-6.9 kpc, and an age of 1 Myr for NGC 3603 Young Cluster (NYC). We identify pre-main-sequence/main-sequence transition stars located in the short-lived radiative-convective gap, which in the NYC occurs in the mass range 3.5-3.8 Msun. We also identify a sparse population of stars with an age of 4 Myr, which appear to be the lower mass counterparts to previously discovered blue supergiants located in the giant HII region NGC 3603. For the first time, we are able to measure the internal velocity dispersion of a starburst cluster from 234 stars with I < 18.5 mag to {\sigma}_pm1D=141+/-27 {\mu}as/yr (4.5+/-0.8 km/s at a distance of 6.75 kpc). As stars with masses between 1.7 and 9 Msun all exhibit the same velocity dispersion, the cluster stars have not yet reached equipartition of kinetic energy (i.e., the cluster is not in virial equilibrium). The results highlight the power of combining high-precision astrometry and photometry, and emphasize the role of NYC as a benchmark object for testing stellar evolution models and dynamical models for young clusters and as a template for extragalactic starburst clusters.