NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer
NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer
复制标题
DOI：
10.1051/0004-6361/201937054
复制
发表时间：
2020-03
影响因子：
6.5
通讯作者：
Y. Osorio;C. Allende-Prieto;I. Hubeny;S. Mészáros;M. Shetrone
中科院分区：
文献类型：
--
作者：
Y. Osorio;C. Allende-Prieto;I. Hubeny;S. Mészáros;M. Shetrone
上下文在模拟恒星光谱时，放松局部热力学平衡（LTE）假设是确定晚型恒星化学丰度优于约10%的必要步骤。目标。我们描述了我们的多元素（Na，Mg，K和Ca）非LTE（NLTE）计算，它可以应用于APOGEE调查。方法.新版本的TLUSTY允许使用预先计算的不透明度表计算冷恒星中的限制NLTE。我们证明，TLUSTY给出了一致的结果与MULTI，一个经过良好测试的代码NLTE在冷星。我们使用TLUSTY来执行LTE和一系列NLTE计算，这些计算同时使用了NLTE中一个、两个、三个和四个元素的所有组合。结果我们考虑到，偏离LTE中的一个元素可以影响其他通过Na，Mg，K和Ca的不透明度的变化。我们发现，原子镁，它提供了强大的紫外线不透明度，并表现出显着偏离LTE在低能量状态，可以影响NLTE人口的钙，导致丰度校正高达0.07德克斯。单元素和多元素情况之间的导出丰度的差异可以超过单元素NLTE测定和LTE分析之间的差异。因此，我们要提醒，这并不总是一个二阶效应。基于对具有可靠大气参数的三颗恒星（大角星、南河三和太阳）的详细测试，我们得出的结论是，我们的NLTE计算提供了丰度修正，对于Ca、Na和K，其光学量可以达到0.1、0.2和0.7 dex，但LTE对Mg来说是一个很好的近似。在H波段，NLTE校正要小得多，并且总是低于0.1 dex。在光学和IR中推导出的NLTE丰度是一致的。在所有三颗恒星中，NLTE谱线轮廓比LTE对应的所有四种元素更适合观测。结论.在电离阶段，过度电离是一种重要的NLTE机制，其中的原子元素可能会受到Mg偏离LTE的影响。在计算H波段线路的NLTE曲线时，必须特别注意用于高位电平的冲突。在光学和H-波段的推导NLTE校正不同，但推导的NLTE丰度是一致的两个光谱区域之间。
Context. Relaxing the assumption of local thermodynamic equilibrium (LTE) in modelling stellar spectra is a necessary step to determine chemical abundances to better than about 10% in late-type stars. Aims. We describe our multi-element (Na, Mg, K, and Ca) non-LTE (NLTE) calculations, which can be applied to the APOGEE survey. Methods. The new version of TLUSTY allows for the calculation of restricted NLTE in cool stars using pre-calculated opacity tables. We demonstrate that TLUSTY gives consistent results with MULTI, a well-tested code for NLTE in cool stars. We used TLUSTY to perform LTE and a series of NLTE calculations that simultaneously used all combinations of one, two, three and four of the elements in NLTE. Results. We take into account that departures from LTE in one element can affect others through changes in the opacities of Na, Mg, K, and Ca. We find that atomic Mg, which provides strong UV opacity and exhibits significant departures from LTE in the low-energy states, can affect the NLTE populations of Ca, leading to abundance corrections as large as 0.07 dex. The differences in the derived abundances between the single-element and the multi-element cases can exceed those between the single-element NLTE determinations and an LTE analysis. We therefore caution that this is not always a second-order effect. Based on detailed tests for three stars with reliable atmospheric parameters (Arcturus, Procyon, and the Sun), we conclude that our NLTE calculations provide abundance corrections that can in the optical amount to 0.1, 0.2, and 0.7 dex for Ca, Na and K, but LTE is a good approximation for Mg. In the H-band, NLTE corrections are much smaller and always lower than 0.1 dex. The derived NLTE abundances in the optical and in the IR are consistent. In all three stars, NLTE line profiles fit the observations better than the LTE counterparts for all four elements. Conclusions. The atomic elements in ionisation stages where over-ionisation is an important NLTE mechanism are likely affected by departures from LTE in Mg. Particular care must be taken with the collisions that are adopted for high-lying levels when NLTE profiles of lines in the H-band are calculated. The derived NLTE corrections in the optical and in the H-band differ, but the derived NLTE abundances are consistent between the two spectral regions.