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首页> 外文期刊>Astronomy and astrophysics >HST/ACS colour–magnitude diagrams of M?31 globular clusters
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HST/ACS colour–magnitude diagrams of M?31 globular clusters

机译：M？31球状星团的HST / ACS色度图

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Aims. With the aim of increasing the sample of M31clusters for which a colour-magnitude diagram is available, we searchedthe HST archive for ACS images containing objects included in theRevised Bologna Catalogue of M31 globular clusters. Methods. Sixty-three such objects were found. We used theACSimages to confirm or revise their classification and were ableto obtain useful CMDs for 11old globular clusters and6luminous young clusters. We obtained simultaneous estimates ofthe distance, reddening, and metallicity of old clusters by comparingtheir observed field-decontaminated CMDs with a grid of templateclusters of the Milky Way. We estimated the age of the young clustersby fitting with theoretical isochrones. Results. For the old clusters, we found metallicities in the range .The individual estimates generally agree with existing spectroscopicestimates. At least four of them display a clear blue horizontalbranch, indicating ages 10Gyr.All six candidate young clusters are found to have ages <1Gyr.The photometry of the clusters is made publicly available through adedicated web page. Conclusions. With the present work the total number of M31GCs with reliable optical CMD increases from 35 to 44 for the oldclusters, and from 7 to 11 for the young ones. The old clusters showsimilar characteristics to those of theMW. We discuss the case ofthe clusterB407, with a metallicity and located at a large projected distance from the centre of M31 (kpc) and from the major axis of the galaxy (Y=11.3kpc).Metal-rich globulars at large galactocentric distances are rare both inM31 and in the Milky Way. B407, in addition, has a velocity instark contrast with the rotation pattern shared by the bulkofM31 clusters of similar metallicity. This, along withother empirical evidence, supports the hypothesis that the cluster(together withB403) is physically associated with a substructurein the halo of M31 that has been interpreted as the relic of amerging event. Key words: galaxies: individual: M31 - galaxies: star clusters - catalog - galaxies: Local Group
机译：目的为了增加可获取其色度图表的M31簇的样本，我们在HST档案库中搜索了ACS图像，其中包含M31球状星团修订版Bologna目录中包含的对象。方法。发现了63个这样的物体。我们使用ACS图像来确认或修改它们的分类，并且能够为11个老球状星团和6个发光年轻星团获得有用的CMD。我们通过将观察到的被现场污染的CMD与银河系的模板簇网格进行比较，获得了对旧星团的距离，变红和金属性的同步估计。我们通过与理论等时线拟合来估计年轻星团的年龄。结果。对于旧的团簇，我们发现金属范围在此范围内。单个估计值通常与现有的光谱估计值一致。其中至少有四个显示清晰的蓝色水平分支，表明年龄为10Gyr。发现所有六个候选年轻星团的年龄小于1Gyr。这些星团的光度法可通过专用网页公开获得。结论。在目前的工作中，具有可靠光学CMD的M31GC的总数从旧集群的35个增加到44个，年轻集群的7个到11个。旧的群集显示出与MW相似的特征。我们讨论了具有金属性并位于距M31中心（kpc）和距星系主轴线（Y = 11.3kpc）较大的投影距离处的B407簇的情况。在较大的银心中心距离处富金属的球状体很少见无论是在M31还是在银河系中。另外，B407与金属相似的M31团簇共享的旋转模式具有鲜明的速度对比。这与其他经验证据一起，支持了这样的假说：该簇（与B403一起）与M31晕圈中的一个子结构物理关联，该子结构已被解释为正在发生的事件的遗迹。关键词：星系：个体：M31-星系：星团-目录-星系：本地群

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