AI 中文总结
本研究构建了从太阳丰度到1/31太阳丰度的OB型恒星大气网格，分析金属丰度对温度诊断线的影响，发现低金属丰度下He I线可作为B型恒星光学波段的主要温度指标，且低金属丰度恒星更易发射硬电离辐射。
AI 中文摘要
大质量热星是宇宙中的主要电离源之一，恒星的电离通量强烈依赖于其温度，而温度最宜通过同一元素不同电离阶段的谱线进行光谱测量。对于O型恒星的定量光谱分析，通常使用氦线；对于B型恒星，则使用硅和镁的谱线。在低金属丰度下，许多用于诊断的金属线会消失。我们对OB型恒星大气模型开展系统理论分析，研究金属丰度对关键温度诊断线的影响，以及这如何影响光谱分类。我们计算了四个不同金属丰度（从太阳丰度到1/31太阳丰度）的大量最先进非局部热动平衡（non-LTE）恒星大气模型网格。我们给出了选定诊断线在温度-引力平面上的等值宽度，并研究它们对金属丰度的依赖关系。利用银河系O型和B型恒星模板，我们建立了用于光谱分类的等值宽度比值，并将其应用于我们的模型。在我们模型网格中最热的恒星中，由于大气中回热减少，氦I（He I）线在更低金属丰度下变得可探测，为其分类开辟了新可能性。用于B型恒星分析的金属线在金属丰度低于小麦哲伦云的恒星光谱中大多缺失，仅硅线除外，这对当前分类方案构成挑战。我们的恒星大气网格显示，金属丰度降低导致许多金属线消失，使得光学波段中B型恒星唯一的温度指标是灵敏度不同的氦I线。OB型恒星的电离通量可能部分被恒星风捕获，因此在更低金属丰度下，更大比例的恒星能够发射硬电离辐射。
英文摘要
Massive hot stars are among the major ionizing sources in the Universe. The ionizing flux of a star strongly depends on its temperature, which is best measured spectroscopically using lines of different ionization stages of the same element. For the quantitative spectral analysis of O-type stars, helium lines are commonly employed, and for B-type stars, lines of silicon and magnesium are used. At low metallicity, many of the diagnostic metal lines disappear. We conduct a systematic theoretical analysis of stellar atmosphere models of OB stars to study the effect of metallicity on key temperature diagnostic lines and how this impacts spectral classification. We computed large grids of state-of-the-art non-LTE stellar atmosphere models at four different metallicities, ranging from solar to 1/31 solar. We presented equivalent widths of selected diagnostic lines in the temperature-gravity plane and investigated their dependence on metallicity. Using Galactic stellar templates of O- and B-type stars, we established equivalent width ratios for spectral classification and applied them to our models. For the hottest stars in our model grids, He I lines become detectable at lower metallicity due to the reduced back-warming in the atmosphere, opening new possibilities for their classification. Metal lines used for the analysis of B-type stars are mostly absent in the spectra of stars with metallicity below that of the Small Magellanic Cloud, except Si lines, challenging current classification schemes. Our stellar atmosphere grids reveal that the decrease in metallicity causes many metal lines to disappear, leaving different sensitivities of He I lines the only temperature indicators for B-type stars in the optical. The ionizing flux of OB-type stars can be partially trapped within the stellar wind. As a result, at lower metallicity, a larger fraction of stars can emit hard ionizing radiation.
Comments16 pages + 4 appendix, 14 Figures, 4 Tables
