银河系疏散星团UBC 274外围的双星序列
A binary star sequence in the outskirts of the disrupting Galactic open cluster UBC 274
摘要：
本文报道了在最近发现的~3 Gyr年龄的疏散星团UBC 274中发现的大量双星。当星系团的颜色-星等图被微分红化校正后，它就变得可见了，并且质量比（q）的范围从0.5到1.0。它的恒星密度径向分布和累积分布作为离星团中心距离的函数显示，它延伸到星团潮汐尾的观测边界（约为星团半径的6倍），其空间分布与星团主序星（MS）的空间分布没有区别。此外，q值小于或大于0.75的双星也没有表现出任何空间分布差异。从盖亚DR 2天体测量和运动学数据，我们计算银河系坐标和空间速度相对于集群的中心和平均集群空间速度，分别。我们发现，所有位于潮汐尾的星团成员，无论是单星还是双星，都移动得相对较快。它们的运动在银河平面上的投影类似于一个旋转的固体，而那些沿着银河中心的径向和垂直于银河平面的方向的运动则表明该星团正在被破坏。星团MS和双星的空间分布和运动学模式的相似性表明，UBC 274正面临着一个强烈的破坏过程，这一过程显然已经清除了内部动力学演化的任何特征，如由两体弛豫驱动的质量分离。
英文摘要：
We report the identification of a numerous binary star population in the recently discovered ~3 Gyr old open cluster UBC 274. It becomes visible once the cluster color-magnitude diagram is corrected by differential reddening and spans mass ratios (q) values from 0.5 up to 1.0. Its stellar density radial profile and cumulative distribution as a function of the distance from the cluster's center reveal that it extends out to the observed boundaries of the cluster's tidal tails (~ 6 times the cluster's radius) following a spatial distribution indistinguishable from that of cluster Main Sequence (MS) stars. Furthermore, binary stars with q values smaller or larger than 0.75 do not show any spatial distribution difference either. From Gaia DR2 astrometric and kinematics data we computed Galactic coordinates and space velocities with respect to the cluster's center and mean cluster space velocity, respectively. We found that, cluster members located all along the tidal tails, irrespective of being a single or binary star, move relatively fast. The projection of their motions on the Galactic plane resembles that of a rotating solid body, while those along the radial direction from the Galactic center and perpendicular to the Galactic plane suggest that the cluster is being disrupted. The similarity of the spatial distributions and kinematic patterns of cluster MS and binary stars reveals that UBC 274 is facing an intense process of disruption that has apparently swept out any signature of internal dynamic evolution like mass segregation driven by two-body relaxation.
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