论文标题
球状簇NGC 2808中紫外线恒星的首次广泛探索
The First Extensive Exploration of UV-bright Stars in the Globular Cluster NGC 2808
论文作者
论文摘要
在这项研究中，我们确定并描述了球状群集NGC 2808中的热和发光的紫外线明星。我们将来自Ultra Violet Imaging望远镜（UVIT）的数据组合在印度太空卫星Astellite，Astrosat，Hubble Space Telescope Space telescope uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv uv un $ \ ang [Angle-symbol-over-decimal] {; 2.7;} \ times \ ang [Angle-Symbol-over-decimal] {; 2.7;} $），Gaia和Gaia和Gaia和地面的光学光度法。我们构建了紫外线和紫外线颜色 - 磁性图，将水平分支（HB）成员与理论零时代的HB和末端 - 年龄HB模型进行了比较，并确定了34个UV-Bright恒星。 UV -Bright星的光谱能量分布安装了理论模型，以估算其有效温度（12500 K -100,000 K），Radii（0.13至2.2 $ r _ {\ odot} $）和发光度（$ \ sim 40 $ 40 $至$ 3000至$ 3000 $ $ L _ {\ odot} $）的第一个时间。然后将这些恒星与理论后Hb（PHB）进化轨迹一起放置在H-R图上，以评估其进化状态。这些模型表明，这些恒星中的大多数处于AGB-Manqual阶段，除三个外，所有恒星都具有进化质量$ <$ 0.53 $ m _ {\ odot} $。我们还计算了该集群中热点后（早期）-AGB（p（e）AGB）恒星的理论上预期的数量，并找到了与我们的观测值相匹配的范围。从Astrosat/Uvit图像中鉴定出的位于簇外部区域的七个紫外线恒星是详细的随访光谱研究的理想候选者。
In this study, we identified and characterized the hot and luminous UV-bright stars in the globular cluster NGC 2808. We combined data from the Ultra Violet Imaging Telescope (UVIT) on-board the Indian space satellite, AstroSat, with the Hubble Space Telescope UV Globular Cluster Survey (HUGS) data for the central region (within $\sim$ $\ang[angle-symbol-over-decimal]{;2.7;} \times \ang[angle-symbol-over-decimal]{;2.7;}$) and Gaia and ground-based optical photometry for the outer parts of the cluster. We constructed the UV and UV-optical color-magnitude diagrams, compared the horizontal branch (HB) members with the theoretical zero-age HB and terminal-age HB models and identified 34 UV-bright stars. The spectral energy distributions of the UV-bright stars were fitted with theoretical models to estimate their effective temperatures (12500 K - 100,000 K), radii (0.13 to 2.2 $R_{\odot}$), and luminosities ($\sim 40$ to $3000$ $L_{\odot}$) for the first time. These stars were then placed on the H-R diagram, along with theoretical post-HB (pHB) evolutionary tracks to assess their evolutionary status. The models suggest that most of these stars are in the AGB-manqué phase and all, except three, have evolutionary masses $<$ 0.53 $M_{\odot}$. We also calculated the theoretically expected number of hot post-(early)-AGB (p(e)AGB) stars in this cluster and found the range to match our observations. Seven UV-bright stars located in the outer region of the cluster, identified from the AstroSat/UVIT images, are ideal candidates for detailed follow-up spectroscopic studies.
