标题： 铬：贫金属星中的非局部热平衡丰度与银河系的核合成 显示英文标题

标题： Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

摘要： 目标。 我们研究了晚型恒星大气中铬的统计平衡，以确定文献中经常遇到的铬I和铬II线之间的系统丰度差异是否由于偏离了局部热平衡（LTE）。 此外，我们试图用太阳邻域的化学演化模型来解释[Cr/Fe]随[Fe/H]的变化趋势。 方法。 我们对铬原子模型进行了非局部热平衡（NLTE）计算，该模型包括总共340个能级和6806个跃迁。我们利用Nahar（2009）的量子力学光电离截面，并研究了模型对不确定的H I碰撞截面的敏感性。NLTE谱线形成用于太阳和10颗金属贫乏恒星（-3.2 < [Fe/H] < -0.5）的MAFAGS-ODF模型大气，通过合成和观测的通量光谱的比较得出铬的丰度。 结果。 如果我们忽略与H I原子的非弹性碰撞，对于具有不同恒星参数的模型，我们实现了良好的铬离子化平衡。基于铬I线的太阳NLTE丰度为5.74 dex，误差为{\sigma }= 0.05 dex；它比LTE丰度高\sim 0.1 dex。 对于金属贫乏的恒星，铬I线的NLTE丰度修正范围从+0.3到+0.5 dex。 得到的[Cr/Fe]比例在此分析的金属丰度范围内大致与太阳一致，这与当前关于超新星中铁峰元素产生的观点是一致的。 结论。 铬相对于铁在金属贫乏恒星中的不足倾向是由于忽略了铬I线形成中的NLTE效应而产生的伪影，与银河系星际介质的特殊物理条件或核合成理论的缺陷无关。 显示英文摘要

摘要： Aims. We investigate statistical equilibrium of Cr in the atmospheres of late-type stars to show whether the systematic abundance discrepancy between Cr I and Cr II lines, as often encountered in the literature, is due to deviations from LTE. Furthermore, we attempt to interpret the NLTE trend of [Cr/Fe] with [Fe/H] using chemical evolution models for the solar neighborhood. Methods. NLTE calculations are performed for the model of Cr atom, comprising 340 levels and 6806 transitions in total. We make use of the quantum-mechanical photoionization cross-sections of Nahar (2009) and investigate sensitivity of the model to uncertain cross-sections for H I collisions. NLTE line formation is performed for the MAFAGS-ODF model atmospheres of the Sun and 10 metal-poor stars with -3.2 < [Fe/H] < -0.5, and abundances of Cr are derived by comparison of the synthetic and observed flux spectra. Results. We achieve good ionization equilibrium of Cr for the models with different stellar parameters, if inelastic collisions with H I atoms are neglected. The solar NLTE abundance based on Cr I lines is 5.74 dex with {\sigma} = 0.05 dex; it is \sim 0.1 higher than the LTE abundance. For the metal-poor stars, the NLTE abundance corrections to Cr I lines range from +0.3 to +0.5 dex. The resulting [Cr/Fe] ratio is roughly solar for the range of metallicities analyzed here, which is consistent with current views on production of these iron peak elements in supernovae. Conclusions. The tendency of Cr to become deficient with respect to Fe in metal-poor stars is an artifact due to neglect of NLTE effects in the line formation of Cr I, and it has no relation to peculiar physical conditions in the Galactic ISM or deficiencies of nucleosynthesis theory.