论文标题
球状簇NGC 1851的水平分支星星中的特殊性：发现EHB恒星的蓝色Straggler伴侣
Peculiarities in the horizontal branch stars of globular cluster NGC 1851: Discovery of a Blue straggler companion to an EHB star
论文作者
论文摘要
我们介绍了使用基于地面和空间的多波长数据，对远紫外线（FUV）明亮的水平分支（HB）星星进行了了解，以了解球状簇NGC 1851的HB序列中的特殊性。光学和紫外线颜色级图用于对HST和GAIA DR2数据的HB恒星及其成员资格进行分类。构建了位于芯到潮汐半径的热HB恒星的光谱能分布（SED）。 SEDS揭示了G-Jump附近的HB恒星在使用大气群集金属性模型进行拟合时显示出FUV通量的减少，但是由于大气扩散，发现具有更高金属性模型的较高金属模型。我们报告了四个特别有趣的极端HB（EHB）恒星，其中两颗在内部和外部区域。我们分别检测到一个亚光EHB和一个“蓝钩”候选者，分别为TEFF约25,000 K和31,000 K。我们发现了一颗EHB恒星（TEFF〜17,000 K），半径位于BHB和正常的EHB星之间。我们的EHB恒星中最特殊的是蓝色Straggler Star（BSS）（TEFF〜7,000 K）的光度二进制，这是光谱研究的重要目标。候选EHB+BSS二进制系统的发现可能有助于解释RGB阶段的质量损失，从而导致EHB恒星的形成。
We present a study of Far Ultraviolet (FUV) bright horizontal branch (HB) stars to understand the peculiarities seen in the HB sequence of the Globular Cluster NGC 1851, using ground and space based multi-wavelength data. Optical and UV color magnitude diagrams are used to classify HB stars and their membership from HST and Gaia DR2 data. The Spectral energy distributions (SEDs) of the hot HB stars located from the core to tidal radii are constructed. The SEDs reveal that the HB stars near the G-jump show a decrease in the FUV flux when atmospheric models of cluster metallicity are used for fitting, but a better fit is found with higher metallicity models, as expected due to atmospheric diffusion. We report on four particularly interesting extreme HB (EHB) stars, two each in inner and outer regions. We detect a sub-luminous EHB and a "blue-Hook" candidates with temperatures Teff ~ 25,000 K and 31,000 K, respectively. We found an EHB star (Teff ~ 17,000 K) with the radius lies between the BHB and normal EHB stars. The most peculiar of our EHB stars (Teff ~ 28,000 K) is found to be a photometric binary to a Blue Straggler star (BSS) (Teff ~ 7,000 K), which is an important target for spectroscopic study. This discovery of the candidate EHB+BSS binary system, could help to explain the mass loss in the RGB phase, leading to the formation of EHB stars.
