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Supra-Horizontal-Branch Stars and Population Gradients in the Galactic Center Globular Cluster NGC 6522*

机译:银河系中心球状星团NGC 6522中的超水平分支星和种群梯度*

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We have imaged the core of NGC 6522 and an adjacent field 1' north in the U and B passbands using the (pre-COSTAR) HST Planetary Camera. We find 13 stars located 1.5 mag above the horizontal branch. These supra-horizontal-branch (SHB) stars have not been noted previously in NGC 6522, although they occur in other globular clusters. The SHB stars' radial distribution appears to be similar to those of the red giants. There are indications that the NGC 6522 core red giants are depleted relative to the horizontal branch stars. The SHB stars may be evolved blue horizontal-branch stars, the tidally stripped cores of red giants, or evolved blue stragglers. There is also a well-populated horizontal branch with a large number of very blue stars; in these passbands the overall color-magnitude diagram resembles that of the core collapse cluster M15.
机译:我们已经使用(COSTAR之前的)HST行星相机对NGC 6522的核心以及U和B通带以北1'的相邻场成像。我们发现13个星位于水平分支上方1.5 mag。尽管它们出现在其他球状星团中,但以前在NGC 6522中没有注意到这些超水平分支(SHB)星。 SHB星的径向分布似乎与红色巨星的径向分布相似。有迹象表明,NGC 6522核心红色巨星相对于水平分支星已经耗尽。 SHB恒星可能是蓝色水平分支的演化恒星,红色巨人的潮汐剥离的核或蓝色散乱的星体。还有一个人口稠密的水平分支,上面有很多非常蓝的星星。在这些通带中,整体的色度图类似于核心坍塌簇M15的色度图。

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