用UV COS / $HST$数据重新考察超贫铁星$~$ 1327-2326的铁丰度
Revisiting the iron abundance in the hyper iron-poor star HE$~$1327-2326 with UV COS/$HST$ data
摘要：
我们提出了一个新的铁丰度分析的超贫金属恒星HE $~$ 1327-2326，根据Fe II线检测到的紫外光谱范围内的第一次。在宇宙起源摄谱仪（Cosmic Origins Spectrograph，COS）的光谱中，可以测量到五条新的Fe II谱线。还首次检测到Si I线。我们确定了一个一维局部热力学平衡（LTE）Fe II丰度[Fe II/H] = -5.99 $\pm$ 0.25。我们还调查偏离LTE的Fe I和Fe II线。通过对其他贫金属恒星的3D非LTE（NLTE）分析，我们确定了HE $~$ 1327-2326中由于缺乏完整的3D NLTE Fe计算而产生的潜在“残余”3D效应。因此，我们采用先前在HE $~$ 1327-2326的光谱中检测到的10条弱Fe I线的测量，因为在我们的UV光谱中没有检测到Fe I线。根据我们先前的工作，我们采用了HE $~$ 1327-2326的1D NLTE Fe I丰度[Fe/H] = -5.20 $\pm$ 0.12。采用基于光学Fe I而不是UV线的值在很大程度上是通过我们对模型大气的广泛研究以及在整个UV光波长范围内对不同线的辐射转移效应而获得的。铁丰度[Fe/H] = -5.20 $\pm$ 0.12仅比之前研究中使用的铁丰度高0.2倍。因此，以前关于恒星性质的结论不会受到影响。
英文摘要：
We present a new iron abundance analysis of the hyper metal-poor star HE$~$1327-2326, based on Fe II lines detected in its UV spectral range for the first time. In a Cosmic Origins Spectrograph (COS) spectrum, five new Fe II lines could be measured. A Si I line was also detected for the first time. We determine a 1D Local Thermodynamic Equilibrium (LTE) Fe II abundance of [Fe II/H] = -5.99$\pm$0.25. We also investigate departures from LTE for both Fe I and Fe II lines. Guided by 3D Non-LTE (NLTE) analyses of other well-studied metal-poor stars, we identify potential "residual" 3D effects in HE$~$1327-2326 arising from the absence of full 3D NLTE Fe calculations. Accordingly, we employ measurements of 10 weak Fe I lines previously detected in an optical spectrum of HE$~$1327-2326, as no Fe I lines are detectable in our UV spectrum. Following our previous work, we adopt the 1D NLTE Fe I abundance of [Fe/H] = -5.20$\pm$0.12 for HE$~$1327-2326. Adopting a value based on the optical Fe I rather than UV lines was heavily informed by our extensive investigation of model atmosphere and radiative transfer effects on different lines accross the entire UV-optical wavelength range. An iron abundance of [Fe/H] = -5.20$\pm$0.12 is only 0.2 dex higher than what was used in previous studies. Accordingly, no previous conclusions regarding the nature of the star are affected.
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