标题： 中性氧谱线形成重新研究：使用新的碰撞数据，在低金属丰度下出现显著的非局部热平衡偏离 显示英文标题

标题： Neutral oxygen spectral line formation revisited with new collisional data: large departures from LTE at low metallicity

摘要： 我们详细研究了在MARCS模型大气中，高激发态中性氧777 nm三重态在晚型恒星（光谱类型F到K）中的非局部热平衡（non-LTE）形成过程。我们使用统计平衡代码MULTI进行了计算，并包括了对元素丰度分析影响的估计。所采用的原子模型特别包括了最近的量子力学电子碰撞数据。我们确认，在晚型恒星中，O I三重态线在非LTE条件下形成，相对于LTE具有负的丰度修正。在低金属丰度情况下，三重态-五重态系统间电子碰撞导致较大的线 opacity，这是一种之前未被考虑或严重低估的耦合形式。对于温度较高的模型（包括巨星和矮星），非LTE效应通常较为严重。有趣的是，在贫金属主序星中，负的非LTE丰度修正倾向于随着金属丰度降低而迅速变得更加严重。当忽略H碰撞时，它们分别在[Fe/H]=-3和[Fe/H]=-3.5时达到约0.9 dex和1.2 dex。即使考虑了这些碰撞，LTE丰度在这些低金属丰度情况下仍然严重高估，分别约为0.5 dex和0.9 dex。尽管不完全了解的非弹性氢碰撞仍然是一个重要不确定性，但大的金属丰度依赖的非LTE效应似乎表明，在贫金属晕星中，与LTE相比，[O/Fe]会较低。 显示英文摘要

摘要： We present a detailed study of the non-Local Thermodynamic Equilibrium (non-LTE) formation of the high-excitation neutral oxygen 777 nm triplet in MARCS model atmospheres representative of late-type stars with spectral types F to K. We carried out the calculations using the statistical equilibrium code MULTI, including estimates of the impact on elemental abundance analysis. The atomic model employed includes, in particular, recent quantum-mechanical electron collision data. We confirm that the O I triplet lines form under non-LTE conditions in late-type stars, suffering negative abundance corrections with respect to LTE. At low metallicity, large line opacity stems from triplet-quintet intersystem electron collisions, a form of coupling previously not considered or seriously underestimated. The non-LTE effects become generally severe for models (both giants and dwarfs) with higher T_eff. Interestingly, in metal-poor turn-off stars, the negative non-LTE abundance corrections tend to rapidly become more severe towards lower metallicity. When neglecting H collisions, they amount to as much as ~ 0.9 dex and ~ 1.2 dex, respectively at [Fe/H]=-3 and [Fe/H]=-3.5. Even when such collisions are included, the LTE abundance remains a serious overestimate, correspondingly by ~ 0.5 dex and ~ 0.9 dex at such low metallicities. Although the poorly known inelastic hydrogen collisions thus remain an important uncertainty, the large metallicity-dependent non-LTE effects seem to point to a resulting "low" (compared to LTE) [O/Fe] in metal-poor halo stars.