标题： 贫金属参考星系列之二。 红巨星和CEMP恒星 显示英文标题

标题： Titans metal-poor reference stars II. Red giants and CEMP stars

摘要： 位于太阳邻域之外的F型、G型和K型恒星的代表性样本已经开始在光谱巡天中可用。金属丰度较低（[Fe/H]~$\lesssim -0.8$~dex）的巨星在较远距离上变得越来越重要。在金属丰度较低的恒星中，基于局部热平衡（LTE）光谱学以及仍然广泛使用的颜色-$T_{\mathrm{eff}}$关系的有效温度($T_{\mathrm{eff}}$)被报道为不准确。有必要重新校准这些$T_{\mathrm{eff}}$标度上的化学丰度，以便在多个可用的巡天中将其统一到同一标准标度上以供同时使用。为此，需要一个完整的标准样本，迄今为止，该样本仅限于少数具有准直接$T_{\mathrm{eff}}$测量的恒星。我们的目标是提供一组经过验证的具有准确大气参数的金属丰度较低的标准恒星样本。我们将47颗巨星加入到Giribaldi等人2021年的金属丰度较低的矮星样本中，从而构成了Titans金属丰度较低的参考星。$T_{\mathrm{eff}}$是通过三维非局部热平衡（3D non-LTE）H$\alpha$模型推导出来的，其准确性通过干涉测量法和红外辐射流量法（IRFM）进行了测试。 表面重力（log$g$）通过拟合Mg I b三重线得到，其准确性通过恒星振荡学进行了检验。 金属丰度使用Fe II线得到，并验证与非局部热平衡（non-LTE）光谱合成得到的[Fe/H]一致。 来自三维非局部热平衡（non-LTE）H$\alpha$的$T_{\mathrm{eff}}$温度与干涉测量和红外流量法（IRFM）温度一致，误差在$\pm$46 K以内。 对于34颗具有最高信噪比（S/N）光谱的恒星，我们达到了$\sim$50 K的精度。 对于log$g$，我们总不确定度达到$\pm$0.15 dex。 对于[Fe/H]，我们得到的总不确定度为$\pm$0.09 dex。 我们发现，在贫金属巨星中，铁线在局部热平衡下的电离平衡并不成立。 显示英文摘要

摘要： Representative samples of F-, G-, K-type stars located out of the Solar Neighbourhood has started to be available in spectroscopic surveys. The fraction of metal-poor ([Fe/H]~$\lesssim -0.8$~dex) giants becomes increasingly relevant to far distances. In metal-poor stars, effective temperatures ($T_{\mathrm{eff}}$) based on LTE spectroscopy and on former colour-$T_{\mathrm{eff}}$ relations of still wide use have been reported to be inaccurate. It is necessary to re-calibrate chemical abundances based on these $T_{\mathrm{eff}}$ scales in the multiple available surveys to bring them to the same standard scale for their simultaneous use. For that, a complete sample of standards is required, which so far, is restricted to a few stars with quasi-direct $T_{\mathrm{eff}}$ measurements. We aim at providing a legacy sample of metal-poor standards with proven accurate atmospheric parameters. We add 47 giants to the sample of metal-poor dwarfs of Giribaldi et al. 2021, thereby constituting the Titans metal-poor reference stars. $T_{\mathrm{eff}}$ was derived by 3D non-LTE H$\alpha$ modelling, whose accuracy was tested against interferometry and InfraRed Flux Method (IRFM). Surface gravity (log $g$) was derived by fitting Mg~I~b triplet lines, whose accuracy was tested against asteroseismology. Metallicity was derived using Fe II lines, which was verified to be identical to the [Fe/H] derived from non-LTE spectral synthesis. $T_{\mathrm{eff}}$ from 3D non-LTE H$\alpha$ is equivalent to interferometric and IRFM temperatures within a $\pm$46~K uncertainty. We achieved precision of $\sim$50~K for 34 stars with spectra with the highest S/N. For log $g$, we achieved a total uncertainty of $\pm$0.15~dex. For [Fe/H], we obtained a total uncertainty of $\pm$0.09~dex. We find that the ionization equilibrium of Fe lines under LTE is not valid in metal-poor giants.