论文标题
使用Astrosat，在球状簇NGC 2808的水平分支中斑点星的紫外光度法
UV photometry of spotted stars in the horizontal branch of the globular cluster NGC 2808 using AstroSat
论文作者
论文摘要
最近对球状簇（GCS）中热（20,000至30,000 K）极端水平分支（EHB）恒星的研究导致发现它们的可变性。建议这种变异性是由恒星表面上磁斑的预计旋转驱动的，预计在较短的波长下具有较高的振幅。在这里，我们使用Astrosat上的紫外线成像望远镜（UVIT）介绍了大型GC NGC 2808中此类热星的分析。我们将紫外线数据与中央区域的Hubble Space望远镜Globular群集调查（HUGS）数据结合使用（在$ \ sim $ \ sim $ 2.7'$ $ \ times $ \ times $ 2.7'$中）和集群外部零件外部的基于地面的光学光度法。我们生成了远处（FUV） - 光学色素磁性图（CMD），在这些图中，我们发现与零时代的水平分支（ZAHB）模型相比，热EHB恒星的群体含量比。比较我们已经报道的可变EHB恒星（Vehbs）的FUV幅度表明，最长的车辆是最微弱的，以及旋转期与斑点恒星的紫外线之间的暂定相关性。为了牢固建立任何相关性，进一步的研究至关重要。
A recent study of hot (20,000 to 30,000 K) extreme horizontal branch (EHB) stars in globular clusters (GCs) has led to the discovery of their variability. It is suggested that this variability is driven by the projected rotation of magnetic spots on the stellar surfaces and is expected to have higher amplitudes at shorter wavelengths. Here, we present the analysis of such hot stars in the massive GC NGC 2808 using the Ultraviolet Imaging Telescope (UVIT), aboard AstroSat. We use the UVIT data in combination with the Hubble Space Telescope UV Globular Cluster Survey (HUGS) data for the central region (within $\sim$ $2.7'$ $\times$ $2.7'$) and ground-based optical photometry for the outer parts of the cluster. We generate the far-UV (FUV) - optical colour-magnitude diagrams (CMDs) and in these we find a population of hot EHB stars fainter than the zero-age horizontal branch (ZAHB) model. A comparison of our FUV magnitudes of the already reported variable EHB stars (vEHBs) shows that the longest period vEHBs are the faintest, along with a tentative correlation between rotation period and UV magnitude of spotted stars. In order to firmly establish any correlation, further study is essential.
