Westerlund 1：绑定或未绑定？
Westerlund 1: bound or unbound?
摘要：
银河系疏散星团韦斯特伦德1（Wd 1）是银河系外年轻大质量星团的理想本地模板，因为它是目前附近唯一一个质量达到10^5 M太阳的年轻星团。这种接近使得空间分辨的研究其恒星星族可行，并允许直接比较其性能与测量的速度色散和动力学质量的空间未解决的河外星系团。最近，我们发表了基于四颗红超巨星光谱的动力学质量估计。我们现在已经确定了另外六颗恒星，它们可以从我们的VLT/ISAAC近红外光谱（CO带头区域接近2.29微米）所覆盖的波长确定径向速度，显着改善了统计。我们结合使用步进和扫描穿过星团中心的狭缝，覆盖了一个区域，其中包括以下合适的光谱类型：四颗红超巨星，五颗黄超巨星和一颗B型发射线恒星。我们测得的速度色散是9.2公里/秒。再加上从档案近红外SOFI-NTT图像中得出的0.86 pc的星系团大小，这产生了1.5x10^5 Msun的动力学质量。将其与通过光度测定法得出的质量进行比较，没有迹象表明该簇目前正在溶解。
英文摘要：
The Galactic open cluster Westerlund 1 (Wd 1) represents the ideal local template for extragalactic young massive star clusters, because it is currently the only nearby young cluster which reaches a mass of around 10^5 Msun. The proximity makes spatially resolved studies of its stellar population feasible, and additionally permits direct comparison of its properties with measurements of velocity dispersion and dynamical mass for spatially unresolved extragalactic clusters. Recently, we published the dynamical mass estimate based on spectra of four red supergiants. We have now identified six additional stars which allow a determination of radial velocity from the wavelength covered in our VLT/ISAAC near-infrared spectra (CO bandhead region near 2.29micron), improving statistics significantly. Using a combination of stepping and scanning the slit across the cluster centre, we covered an area which included the following suitable spectral types: four red supergiants, five yellow hypergiants, and one B-type emission line star. Our measured velocity dispersion is 9.2 km/s. Together with the cluster size of 0.86 pc, derived from archival near-infrared SOFI-NTT images, this yields a dynamical mass of 1.5x10^5 Msun. Comparing this to the mass derived via photometry, there is no indication that the cluster is currently undergoing dissolution.
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