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.

最近对球状星团 (GC) 中的热 (20,000 至 30,000 K) 极端水平分支 (EHB) 恒星的研究发现了它们的可变性。有人认为，这种变化是由恒星表面磁点的投影旋转驱动的，预计在较短的波长下具有更高的振幅。在这里，我们展示了使用 AstroSat 上的紫外成像望远镜 (UVIT) 对大质量 GC NGC 2808 中的这些热恒星进行的分析。我们将 UVIT 数据与中心区域的哈勃太空望远镜UV 球状星团调查 (HUGS) 数据结合使用（在\(\sim \) \(2.7'\) \(\times \) \(2.7'\) 内）) 和星团外部的地面光学测光。我们生成了远紫外 (FUV) 光学色等图 (CMD)，在这些图中我们发现了比零年龄水平分支 (ZAHB) 模型更暗的热 EHB 恒星群。对我们已经报道的变 EHB 星 (vEHBs) 的 FUV 星等的比较表明，最长周期的 vEHBs 是最暗的，以及旋转周期和斑点恒星的紫外星等之间的初步相关性。为了牢固地建立任何相关性，进一步研究是必不可少的。