A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars ?
A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars ?
复制标题
DOI：
10.1051/0004-6361/201015336
复制
发表时间：
2011-01
影响因子：
6.5
通讯作者：
L. Mashonkina;T. Gehren;Jian-rong Shi;A. Korn;F. Grupp
中科院分区：
文献类型：
--
作者：
L. Mashonkina;T. Gehren;Jian-rong Shi;A. Korn;F. Grupp
目标。我们评估非本地的热平衡（非LTE）线形成的两种离子的铁和检查的Fe i和Fe ii之间的电离平衡的模型大气中的冷参考星的基础上最好的可用的完整的模型原子中性和单电离铁。方法.我们提出了一个全面的模型原子铁超过3000测量和预测的能级。作为改进的模型原子的测试和首次应用，铁丰度测定了太阳和五颗恒星的恒星参数和高质量的观测光谱。通过考察氢原子对所选恒星Fe i和Fe ii谱线的不同影响，经验地估算了铁统计平衡中氢原子的非弹性碰撞效率.结果Non-LTE导致Fe i线的系统性耗尽总吸收和正的丰度修正，与以前的研究一致，但是，这种修正的幅度较小，与以前的结果相比。对于太阳金属丰度和轻度金属缺乏的恒星，这些非LTE修正不超过0.1 dex，而对于非常缺乏金属的恒星HD 84937和HD 122563，它们分别在0.21 dex和0.35 dex之间变化，这取决于假设的与氢原子碰撞的效率。基于对这两颗星的Fe i/Fe ii电离平衡的分析，我们建议在Fe的非LTE研究中应用Drawin形式主义，比例因子为0.1。对于铁二行非LTE的修正不超过0.01德克斯的绝对值在整个范围内的恒星参数被认为是。这项研究揭示了两个问题。第一个问题是Fe i和Fe ii谱线的gf值不够精确，不足以进行高精度的绝对恒星丰度测定。对于太阳，从54条Fe i线获得的平均非LTE丰度为7.56 ± 0.09，从18条Fe ii线获得的平均丰度在7.41 ± 0.11和7.56 ± 0.05之间变化，取决于gf值的来源。第二个问题是，Fe i的线给出，平均而言，0.1德克斯低丰度相比，Fe ii线HD 61421和HD 102870，即使应用差分逐线分析方面的太阳。中性原子和第一离子之间的差距点恒星大气建模或/和有效的温度测定的问题。
Aims. We evaluate non-local thermodynamical equilibrium (non-LTE) line formation for the two ions of iron and check the ionization equilibrium between Fe i and Fe ii in model atmospheres of the cool reference stars based on the best available complete model atom for neutral and singly-ionized iron. Methods. We present a comprehensive model atom for Fe with more than 3000 measured and predicted energy levels. As a test and first application of the improved model atom, iron abundances are determined for the Sun and five stars with well determined stellar parameters and high-quality observed spectra. The efficiency of inelastic collisions with hydrogen atoms in the statistical equilibrium of iron is empirically estimated from inspection of their different influence on the Fe i and Fe ii lines in the selected stars. Results. Non-LTE leads to systematically depleted total absorption in the Fe i lines and to positive abundance corrections in agreement with the previous studies, however, the magnitude of such corrections is smaller compared to the earlier results. These non-LTE corrections do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars HD 84937 and HD 122563, respectively, depending on the assumed efficiency of collisions with hydrogen atoms. Based on the analysis of the Fe i/Fe ii ionization equilibrium in these two stars, we recommend to apply the Drawin formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe ii lines non-LTE corrections do not exceed 0.01 dex in absolute value over the whole range of stellar parameters that are considered. This study reveals two problems. The first one is that gf -values available for the Fe i and Fe ii lines are not accurate enough to pursue high-accuracy absolute stellar abundance determinations. For the Sun, the mean non-LTE abundance obtained from 54 Fe i lines is 7.56 ± 0.09 and the mean abundance from 18 Fe ii lines varies between 7.41 ± 0.11 and 7.56 ± 0.05 depending on the source of the gf -values. The second problem is that lines of Fe i give, on average, a 0.1 dex lower abundance compared with those of Fe ii lines for HD 61421 and HD 102870, even when applying a differential line-by-line analysis with regard to the Sun. A disparity between neutral atoms and first ions points to problems of stellar atmosphere modelling or/and effective temperature determination.