Barium is a key element in constraining the evolution of the (not well understood) r-process in the first galactic stars and currently the Ba abundances in these very metal-poor stars were mostly measured under the Local Thermodynamical Equilibrium (LTE) assumption, which may lead in general to an underestimation of Ba. We present here determinations of the barium abundance taking into account the non-LTE (NLTE) effects in a sample of extremely metal-poor stars (EMP stars): 6 turnoff stars and 35 giants. The NLTE profiles of the three unblended Ba II lines (455.4, 585.3, 649.6nm) have been computed. The computations were made with a modified version of the MULTI code, applied to an atomic model of the Ba atom with 31 levels of Ba I, 101 levels of Ba II, and compared to the observations. The ratios of the NLTE abundances of barium relative to Fe are slightly shifted towards the solar ratio. In the plot of [Ba/Fe] versus [Fe/H], the slope of the regression line is slightly reduced as is the scatter. In the interval -3.3 <[Fe/H] < -2.6, [Ba/Fe] decreases with a slope of about 1.4 and a scatter close to 0.44. For [Fe/H] <-3.3 the number of stars is not sufficient to decide whether [Ba/Fe] keeps decreasing (and then CD-38:245 should be considered as a peculiar "barium-rich star") or if a plateau is reached as soon as [Ba/Fe] ~ -1. In both cases the scatter remains quite large, larger than what can be accounted for by the measurement and determination errors, suggesting the influence of a complex process of Ba production, and/or inefficient mixing in the early Galaxy.
Observational constraints on the origin of the elements. IX. 3D NLTE abundances of metals in the context of Galactic Chemical Evolution Models and 4MOST
A Systematic NLTE Study of Very Metal-Poor Stars with Metallicity Down to $-4.3$ dex. II. Lithium Abundance and New Insight to the Lithium Plateau
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Department of Physics, Hebei Normal University（河北师范大学物理学院）
Classical Cepheids in the Galactic thin disk I. Abundance gradients via non-local thermodynamic equilibrium spectral analysis
Università di Roma Tor Vergata（罗马第二大学）；INAF – Osservatorio Astronomico di Roma（罗马天文台）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；ASI - Space Science Data Center（意大利航天局空间科学数据中心）；University of Hawai’i at Manoa（夏威夷大学马诺阿分校）；INAF – Osservatorio Astrofisico di Torino（都灵天文台）；Texas Christian University（得克萨斯基督教大学）；INAF -- Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（博洛尼亚天文物理与空间科学观测站）；Sapienza Università di Roma（罗马第一大学）；INAF - Osservatorio Astronomico di Capodimonte（卡波迪蒙特天文台）；Parthenope University of Naples（那不勒斯帕泰诺佩大学）；Università degli Studi di Bologna（博洛尼亚大学）；The University of Tokyo（东京大学）；Universidad de La Laguna（拉古纳大学）；Odessa National University（敖德萨国立大学）
Determination of Sodium Abundance Ratio from Low-Resolution Stellar Spectra and Its Applications
本文提出了一种利用低分辨率（$R \sim$ 2000）恒星光谱中的Na I-D双重线确定钠丰度比（[Na/Fe]）的方法。由于恒星Na I D线与星际介质（ISM）产生的Na I D线混合，我们发展了一种利用与$E(B-V)$成正比的消光和星际Na I D吸收线的等效宽度（EW）之间的关系来去除星际Na I D线的技术。在测量[Na/Fe]时，我们还考虑了非局部热力学平衡（NLTE）效应的校正。与高分辨率光谱巡天数据的比较表明，对于[Fe/H] $>$ $-$ 3.0的恒星，低分辨率光谱[Na/Fe]的预期精度优于0.3 dex。我们还提出了一个简单的应用程序，采用估计的[Na/Fe]值为大量的恒星光谱从斯隆数字巡天（SDSS）。在将SDSS星分为Na正常、Na高和Na极端三种类型后，我们探讨了它们与银河系球状星团（GC）中恒星的关系。我们发现，虽然钠高SDSS星表现出类似的金属丰度分布函数（ψ）的GC，这表明大多数这样的恒星可能起源于GC碎片，钠正常SDSS星的ψ遵循典型的磁盘和晕星。由于在Na-极端恒星中有很高比例的碳增强贫金属恒星，它们可能具有非GC起源，可能是由于演化的双星伴星的质量转移事件。
The \emph{R}-process Alliance: A Bright, Strongly \emph{R}-process-enhanced Extremely Metal-poor Star Observed with GHOST
Massachusetts Institute of Technology（麻省理工学院）；Joint Institute for Nuclear Astrophysics, Center for the Evolution of the Elements (JINA-CEE)（核天体物理联合研究所，元素演化中心）；NSF NOIRLab（美国国家光学红外天文研究实验室）；University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics（卡弗里宇宙物理学研究所）
