Oxygen line formation in late-F through early-K disk/halo stars. Infrared O I triplet and [O I] lines
Oxygen line formation in late-F through early-K disk/halo stars. Infrared O I triplet and [O I] lines
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DOI：
10.1051/0004-6361:20030217
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发表时间：
2001-05
影响因子：
6.5
通讯作者：
Y. Takeda
中科院分区：
文献类型：
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作者：
Y. Takeda
为了研究O 7771-5和（O）6300/6363谱线的形成，对中性原子氧进行了广泛的非LTE计算，这些计算适用于不同演化阶段的早K到晚F晕/盘星。三重态O跃迁线的形成可以用经典的二能级原子散射模型很好地描述，而非LTE校正实际上是由线跃迁本身的参数决定的，与氧原子模型的细节没有任何显著的相关性。这就简化了问题，因为如果大气参数Teff、log g和λ都已给出，非LTE丰度校正基本上只由谱线强度（Wλ）决定，而不与金属丰度有任何明确的相关性;因此，可以使用列表数值系数的有用解析公式。另一方面，我们的计算导致的强大的结论，LTE是完全有效的禁止（O）线。通过对已发表的来自不同文献的O 7771-5和（O）6300/6363等宽数据的再分析，得出结论：虽然在盘星上观测到了O和（O）丰度的合理一致性，（−1 <（Fe/H）< 0），在明显贫金属晕星中，O-10和（O-12）线之间存在系统的丰度差异（−3 <（Fe/H）< −1），而不被我们的非LTE校正所去除，即，前者比后者大20%。3d ex at−3 <（Fe/H）< −2.对这种不一致性的参数依赖性的检验表明，对于Teff/ log g较高的恒星，这种不一致性的程度往往相对减小，这表明在研究贫金属恒星的氧丰度时更倾向于选择矮星（或亚巨星）。
In order to investigate the formation of O 7771-5 and (O ) 6300/6363 lines, extensive non-LTE calculations for neutral atomic oxygen were carried out for wide ranges of model atmosphere parameters, which are applicable to early-K through late-F halo/disk stars of various evolutionary stages. The formation of the triplet O lines was found to be well described by the classical two-level-atom scattering model, and the non-LTE correction is practically determined by the parameters of the line-transition itself without any significant relevance to the details of the oxygen atomic model. This simplifies the problem in the sense that the non-LTE abundance correction is essentially determined only by the line-strength (Wλ), if the atmospheric parameters of Teff, log g, and ξ are given, without any explicit dependence of the metallicity; thus allowing a useful analytical formula with tabulated numerical coefficients. On the other hand, our calculations lead to the robust conclusion that LTE is totally valid for the forbidden (O ) lines. An extensive reanalysis of published equivalent-width data of O 7771-5 and (O ) 6300/6363 taken from various literature resulted in the conclusion that, while a reasonable consistency of O and (O ) abundances was observed for disk stars (−1 < (Fe/H) < 0), the existence of a systematic abundance discrepancy was confirmed between O and (O ) lines in conspicuously metal-poor halo stars (−3 < (Fe/H) < −1) without being removed by our non-LTE corrections, i.e., the former being larger by ∼0. 3d ex at−3 < (Fe/H) < −2. An inspection of the parameter-dependence of this discordance indicates that the extent of the discrepancy tends to be com- paratively lessened for higher Teff/ log g stars, suggesting the preference of dwarf (or subgiant) stars for studying the oxygen abundances of metal-poor stars.