We provide the first reference framework for extremely metal-poor (XMP) OB-type stars. We parsed a grid of 0.10 $Z_{\odot}$ FASTWIND models, covering the parameter space of O stars and early-B supergiants, through contemporary spectral classification criteria to deliver a calibration of key stellar properties as a function of spectral type, and tabulated colours for the most common photometric systems. By using an extensive grid of models, we account for the different combinations of stellar parameters that result in the same spectral morphology and provide a range of parameters and colours compatible with each spectral subtype and luminosity class. We supply updated photometric criteria to optimize candidate selection of OB stars in XMP environments. We find 0.10 $Z_{\odot}$ OB stars are 1-6 kK hotter and produce higher ionizing fluxes than their Galactic analogues. In addition, we find a bimodal distribution of the HeII-ionizing flux with spectral type; because of its known dependence on effective temperature and the wind, $\log~q_{HeII}$ for individual XMP late-O type stars could be underestimated by up to 4 orders of magnitude by other calibrations, some of them used by population synthesis codes. Finally, we used our calibrated colours to map the extinction of the 0.10 $Z_{\odot}$ galaxy Sextans A finding that reddening is non-negligible and uneven.
Models for Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. II. Application to the Colour-Magnitude Diagrams of the Globular Clusters 47 Tuc, NGC 6362, M5, M3, M55, and M92
我们用HST Wide Field Camera 3（WFC 3）对球状星团（GC）47 Tuc、NGC 6362、M5、M5、M55和M92的观测结果，比较了在C：N：O丰度比（[CNO/Fe]的两个不同值）变化下计算的-2.5 <= [Fe/H] <= -0.5的恒星模型。用于将模型转置到观察平面的测辐射热校正是基于新的MARCS合成光谱，该合成光谱结合了对涉及C、N和O原子的分子的改进处理。在距离模量和红度得到充分支持的假设下，其他α元素的[O/Fe] = 0.6和[m/Fe] = 0.4的等时线（这是GC中双星所青睐的）通常再现了观测到的颜色星等图（CMD）的主要特征，误差在~ 0.03 mag.它们似乎与观测到的（M_F336 W-M_F438 W）_0颜色的分布很好地匹配，这些颜色由CN-弱和CN-强恒星沿低巨星分支跨越，但不是最蓝的巨星，它们被怀疑是贫N的（[N/Fe] <~ -0.5）。无论是（M_F438 W-M_F606 W）_0的绝对颜色，还是在给定的M_F606W星等上这些颜色的变化，都很难解释，除非最红的恒星是富C的（[C/Fe] >~ +0.5）。允许适度的He丰度变化（Δ Y ~ 0.05）改善了对观测的拟合。
Models of Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. I. Bolometric Corrections Derived from New MARCS Synthetic Spectra and Their Implications for Observed Colour-Magnitude Diagrams
新的，高分辨率的MARCS合成光谱已经计算了十几种金属的混合物，允许，反过来，在C：N：O，[CNO/Fe]的变化，和C，O，Mg和Si的丰度增加。目前使用的许多宽带滤波器的辐射热校正（BC）已经从这些光谱中产生。由于改进的处理分子，涉及原子的C，N和O，紫外线和蓝色通带的BC，特别是，从以前的MARCS模型中得到的那些有很大的不同。这些差异，以及不同的金属丰度对BC的影响，在一些指导性的图中显示。还计算了不同混合物在-2.5 <= [Fe/H] <= -0.5时的恒星演化网格。基于这些径迹的等时线在理论H-R图和几个颜色-星等图上进行了相互比较，这些颜色-星等图可以由HST Wide Field Camera 3（WFC 3）F336 W、F438 W、F606 W、F814 W、F110 W和F160 W观测值构造。作为这些模型的首次应用，等时线已被拟合到HST紫外遗产巡天球状星团NGC 6496的WFC 3测光中，得到了非常令人鼓舞的结果。
Models for Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. III. Grids of Isochrones for $-2.5 \le$ [Fe/H] $\le -0.5$ and Helium Abundances $Y = 0.25$ and $0.29$ at Each Metallicity
Empirical colour--effective temperature relations in the SDSS system from IRFM temperatures of GALAH and APOGEE stars
Yunnan Astronomical Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天体物理与天文研究学院）；International Centre of Supernovae (ICESUN)（超新星国际中心）；University of the Chinese Academy of Sciences（中国科学院大学）；CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台光学天文重点实验室）
Extending the [C/N]-Age Calibration: Using Globular Clusters to Explore Older and Metal-Poor Populations
Texas Christian University（德克萨斯基督教大学）；Emory University（埃默里大学）；Whitman College（惠特曼学院）；University of Florida（佛罗里达大学）；Vanderbilt University（范德堡大学）；University of California Observatories, University of California Santa Cruz（加州大学天文台，加州大学圣克鲁兹分校）
Spectroscopic characterization of a sample of metal-poor solar-type stars from the HARPS planet search program. Precise spectroscopic parameters and mass estimation
Discovery of long-period variable stars in the very-metal-poor globular cluster M15
我们在银河系中最贫金属的球状星团M15的巨支星中寻找长周期变星。我们使用多色光学测光从0.6米基尔桑顿和2米利物浦望远镜。在K757和K825中检测到的Δ V ~ 0.15等的变化超过了近一年的异常长的时间尺度，使它们成为银河系球状星团中发现的最贫金属的LPV。K825位于长的第二周期序列上，被认为是富含金属的LPV，尽管没有检测到主周期。我们讨论这种变化的背景下，尘埃生产和恒星演化在低金属丰度，使用额外的光谱从6.5米麦哲伦（拉斯坎帕纳斯）望远镜。尽管存在气体质量损失，但缺乏尘埃生产，这引起了关于尘埃生产和星团内介质的问题。
