HE 1327-2326，一颗未演化的恒星，[Fe/H] < -5.0 III。它的大气层反映了它的天然成分吗？
HE 1327-2326, an unevolved star with [Fe/H] < -5.0 III. Does Its Atmosphere Reflect Its Natal Composition?
摘要：
基于NLTE谱线形成的光谱约束，我们探讨了超贫金属（HMP）星HE 1327-2326的恒星参数（T_eff和log g）的可能范围。结合巴耳末线轮廓和钙I/II电离平衡的限制，一个亚巨星阶段的演变表示。这一结果进一步支持分光光度法观测的巴耳末跳跃。如果使用更高的T_eff值（如一些光度校准所支持的），光谱分析将指示演化的转折点阶段。使用恒星结构的代码，详细处理整个恒星的原子扩散的影响，我们发展了一个低质量的模型恒星，达到HR图的位置HE 1327-2326后，大约13 Gyr。虽然表面丰度的修改显着（超过1德克斯的情况下，不受抑制的扩散），这样的校正不能解决之间的差异推断从未检测到的Li I共振线在6707埃和WMAP为基础的原始锂丰度。由于有许多过程可以破坏锂，任何宇宙学解释的锂丰度低于预期的最低金属丰度将不得不等待未进化的超金属贫恒星的样本大小是一个数量级。关于原子扩散修正的情况仍然同样没有定论。在这里，必须尝试更好地约束内部混合过程，无论是观测和复杂的建模手段。从最近的球状星团研究采取额外的混合过程的限制，最有可能的情况是，HE 1327-2326的表面丰度经历了温和的耗尽（0.2德克斯的顺序）。
英文摘要：
Based on spectroscopic constraints derived from NLTE line formation, we explore the likely range of stellar parameters (T_eff and log g) for the hyper-metal-poor (HMP) star HE 1327-2326. Combining the constraints from Balmer line profiles and the Ca I/II ionization equilibrium, a subgiant stage of evolution is indicated. This result is further supported by spectrophotometric observations of the Balmer jump. If a higher T_eff value was used (as favoured by some photometric calibrations), the spectroscopic analysis would indicate a turnoff-point stage of evolution. Using a stellar-structure code that treats the effects of atomic diffusion throughout the star in detail, we evolve a low-mass model star to reach the HR-diagram position of HE 1327-2326 after roughly 13 Gyr. While the surface abundances are modified significantly (by more than 1 dex for the case of uninhibited diffusion), such corrections can not resolve the discrepancy between the abundance inferred from the non-detection of the Li I resonance line at 6707 Angstroem and the WMAP-based primordial lithium abundance. As there are numerous processes that can destroy lithium, any cosmological interpretation of a lower-than-expected lithium abundance at the lowest metallicities will have to await sample sizes of unevolved hyper-metal-poor stars that are one order of magnitude larger. The situation remains equally inconclusive concerning atomic-diffusion corrections. Here, attempts have to be made to better constrain internal mixing processes, both observationally and by means of sophisticated modelling. With constraints on additional mixing processes taken from a recent globular-cluster study, the likeliest scenario is that HE 1327-2326's surface abundances have undergone mild depletion (of order 0.2 dex).
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