Variable stars in the VVV globular clusters II. NGC 6441, NGC 6569, NGC 6626 (M 28), NGC 6656 (M 22), 2MASS-GC 02, and Terzan 10
Variable stars in the VVV globular clusters II. NGC 6441, NGC 6569, NGC 6626 (M 28), NGC 6656 (M 22), 2MASS-GC 02, and Terzan 10
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VVV 球状星团 II 中的变星。
DOI：
10.1051/0004-6361/202140546
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发表时间：
2021
影响因子：
6.5
通讯作者：
Alonso-García J
中科院分区：
文献类型：
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作者：
Alonso-García J
背景位于银河系内部区域的银河系球状星系团(GGC)遭受高度灭绝，这给它们的观测带来了挑战。周围高密度的场星使他们的研究变得更加复杂。Via Lacta(VVV)观测中的Vista变星提供了一种在消光效应高度减弱的近红外中探索这些GGC的方法。目的我们利用VVV调查提供的独特的多历元、广视场、近红外光度测量技术，在几个内部GGC中寻找变星。我们对探测经典脉动子特别感兴趣，这将有助于我们限制这些GGC的物理参数。在这篇系列文章的第二篇中，我们重点讨论了NGC6656(M22)、NGC6626(M28)、NGC6569和NGC6441；这四个大质量的GGC具有已知的可变来源，但金属丰度却截然不同。我们还回顾了本系列第一篇论文中研究的两个GGC，即2MASS-GC 02和Terzan 10。方法我们提出了一种改进的方法和一个新的参数，可以有效地识别GGC中的变量候选。我们还利用这些探测到的可变星的自身运动及其在天空中的位置和颜色-星等图来指定GGC的成员资格。结果我们在近红外中识别并参数化了所研究的GGC中的众多可变源，编目了数十颗以前未被探测到的可变星。我们在这些星系团中恢复了许多已知的经典脉动子，包括它们绝大多数的基模天琴座RR。我们使用这些脉冲器来获得这些物体的距离和消光。天琴座RR的周期-光度-金属度关系的重新校准使这些GGC的距离与Gaia所报道的更接近，但NGC6441除外，它是一种不常见的Oosterhoff III GGC。这些GGC恢复的自行也与Gaia报告的一致，除了2MASS-GC 02，我们样本中最红的GGC，其中VVV近红外测量提供了更准确的其自行确定。
ContextThe Galactic globular clusters (GGCs) located in the inner regions of the Milky Way suffer from high extinction that makes their observation challenging. High densities of field stars in their surroundings complicate their study even more. The VISTA Variables in the Via Lactea (VVV) survey provides a way to explore these GGCs in the near-infrared where extinction effects are highly diminished.AimsWe conduct a search for variable stars in several inner GGCs, taking advantage of the unique multi-epoch, wide-field, near-infrared photometry provided by the VVV survey. We are especially interested in detecting classical pulsators that will help us constrain the physical parameters of these GGCs. In this paper, the second of a series, we focus on NGC 6656 (M 22), NGC 6626 (M 28), NGC 6569, and NGC 6441; these four massive GGCs have known variable sources, but quite different metallicities. We also revisit 2MASS-GC 02 and Terzan 10, the two GGCs studied in the first paper of this series.MethodsWe present an improved method and a new parameter that efficiently identify variable candidates in the GGCs. We also use the proper motions of those detected variable candidates and their positions in the sky and in the color-magnitude diagrams to assign membership to the GGCs.ResultsWe identify and parametrize in the near-infrared numerous variable sources in the studied GGCs, cataloging tens of previously undetected variable stars. We recover many known classical pulsators in these clusters, including the vast majority of their fundamental mode RR Lyrae. We use these pulsators to obtain distances and extinctions toward these objects. Recalibrated period–luminosity–metallicity relations for the RR Lyrae bring the distances to these GGCs to a closer agreement with those reported byGaia, except for NGC 6441, which is an uncommon Oosterhoff III GGC. Recovered proper motions for these GGCs also agree with those reported byGaia, except for 2MASS-GC 02, the most reddened GGC in our sample, where the VVV near-infrared measurements provide a more accurate determination of its proper motions.