在中等集群质量下探测LMC年龄差距
Probing the LMC age gap at intermediate cluster masses
摘要：
大麦哲伦星系有一个丰富的星团系统，跨越了广泛的年龄和质量。大麦哲伦星系团系统的一个显著特征是存在3-10光年的年龄差距。但这一特征在场星中并不明显。用南方天文物理研究望远镜（SOAR）的光学成像仪（SOI）在英属维尔京群岛拍摄了三个包含相对贫乏和稀疏星团的LMC场，它们的综合颜色与中间年龄简单恒星星族一致。在这些场中总共研究了6个星系团，其中5个估计的初始质量M < 10^4M_sun。进行光度测定，并使用标准点扩散函数拟合方法构建色幅图（CMD）。测量到的最暗的恒星达到V ~ 23。CMD通过利用三维颜色和星等空间来清除场污染，以便选择相对于场过量的恒星。为此，开发了统计CMD比较方法。减法已被证明是成功的，产生清洁的CMD与简单的恒星星族一致。中间年龄的候选人被发现是最古老的在我们的样本中，年龄在1-2 Gyrs之间。在SOAR/SOI中发现的其余星团的年龄从1亿到2亿年不等。我们的分析已经得出结论，我们研究的相对低质量的集群不属于LMC年龄差距。
英文摘要：
The LMC has a rich star cluster system spanning a wide range of ages and masses. One striking feature of the LMC cluster system is the existence of an age gap between 3-10 Gyrs. But this feature is not as clearly seen among field stars. Three LMC fields containing relatively poor and sparse clusters whose integrated colours are consistent with those of intermediate age simple stellar populations have been imaged in BVI with the Optical Imager (SOI) at the Southern Telescope for Astrophysical Research (SOAR). A total of 6 clusters, 5 of them with estimated initial masses M < 10^4M_sun, were studied in these fields. Photometry was performed and Colour-Magnitude Diagrams (CMD) were built using standard point spread function fitting methods. The faintest stars measured reach V ~ 23. The CMD was cleaned from field contamination by making use of the three-dimensional colour and magnitude space available in order to select stars in excess relative to the field. A statistical CMD comparison method was developed for this purpose. The subtraction method has proven to be successful, yielding cleaned CMDs consistent with a simple stellar population. The intermediate age candidates were found to be the oldest in our sample, with ages between 1-2 Gyrs. The remaining clusters found in the SOAR/SOI have ages ranging from 100 to 200 Myrs. Our analysis has conclusively shown that none of the relatively low-mass clusters studied by us belongs to the LMC age-gap.
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