The high excitation levels that form the O i and C i lines seen in RR Lyrae stars have long been known not to obey local thermodynamic equilibrium (LTE) statistics. We have observed 21 RR Lyrae and related stars with the Apache Point Observatory echelle spectrograph on the 3.5‐m telescope and, for the first time, have derived abundances using non‐local thermodynamic equilibrium (NLTE) analyses in conjunction with spectral synthesis. In our previous investigation, we determined carbon to be overabundant using an LTE analysis. We now find the carbon abundance to be underabundant relative to solar abundance for stars with [Fe/H] < 0.0 ([C/Fe] < 0 and by implication [C/H] < 0). Abundances derived for C using an NLTE analysis are consistent with both main‐sequence stars and red giants. This supports the predictions by He flash hydrodynamic simulations, which predict no convective mixing that might bring carbon produced in the He flash to the atmosphere. For oxygen, we find the dependence of [O/Fe] on [Fe/H] to be similar to other stars with [Fe/H] from 0.0 to −2.8.

中文翻译：

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RR lyrae星中的NLTE C和O丰度

形成将O的高激励水平我和C我线天琴座RR分看到人们早已知道不服从本地热力学平衡（LTE）的统计信息。我们使用3.5米望远镜上的Apache Point天文台echelle光谱仪观测到21 RR Lyrae和相关恒星，并且首次使用非本地热力学平衡（NLTE）分析结合光谱合成来得出丰度。在我们之前的调查中，我们使用LTE分析确定了碳过多。现在，对于[Fe / H] <  0.0（[C / Fe]  <  0并暗示[C / H]  <0）的恒星，我们发现相对于太阳丰度而言，碳丰度不足 ）。使用NLTE分析得出的C丰度与主序星和红色巨星都一致。这支持了He闪光流体动力学模拟的预测，该预测没有预测可能将He闪光中产生的碳带入大气的对流混合。对于氧气，我们发现[O / Fe]对[Fe / H]的依赖性与[Fe / H]从0.0到-2.8的其他恒星相似。