填补空白：旧星团的新类别？
Filling the gap: a new class of old star cluster?
摘要：
目前还不清楚长寿星团是否具有连续的大小和质量（以及密度），或者如果是这样，它们应该被认为是具有不同起源的不同类型。利用哈勃太空望远镜（HST）测量大小，并在Keck 10米望远镜上长时间曝光以获得距离，我们发现了第一个确认的星团，这些星团位于Hwang等人（2011）先前声称的大小-光度差距内，称为“回避区”。这些星团的存在扩展了星团的大小、质量和密度的范围，并与当前预测明确的大小-质量关系的形成模型（如剥离的核、巨型球状星团或合并的星团）相矛盾。这些间隙天体的红色表明它们不是一类新的天体，而是与在附近的透镜星系中观察到的微弱模糊有关。我们还报告了一些低光度UCD的大小高达50 pc。现在已经知道星团具有连续的结构特性，未来的统计上完整的研究将受到鼓励。
英文摘要：
It is not understood whether long-lived star clusters possess a continuous range of sizes and masses (and hence densities), or if rather, they should be considered as distinct types with different origins. Utilizing the Hubble Space Telescope (HST) to measure sizes, and long exposures on the Keck 10m telescope to obtain distances, we have discovered the first confirmed star clusters that lie within a previously claimed size-luminosity gap dubbed the `avoidance zone' by Hwang et al (2011). The existence of these star clusters extends the range of sizes, masses and densities for star clusters, and argues against current formation models that predict well-defined size-mass relationships (such as stripped nuclei, giant globular clusters or merged star clusters). The red colours of these gap objects suggests that they are not a new class of object but are related to Faint Fuzzies observed in nearby lenticular galaxies. We also report a number of low luminosity UCDs with sizes of up to 50 pc. Future, statistically complete, studies will be encouraged now that it is known that star clusters possess a continuous range of structural properties.
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