For the first time, a direct non-local thermodynamic equilibrium (NLTE) analysis of carbon and nitrogen lines in the spectra of nine RR Lyrae stars was carried out. We have determined the abundances of these elements together with oxygen, and have shown that the nitrogen content is increased in metallicity-deficient program stars. We conclude that this is a sign of the first dredge up, which occurred at the previous stage of the red giant branch, and brought material processed in an incomplete carbon, nitrogen, oxygen (CNO) cycle to the surface of the star. This effect is significantly enhanced by thermohaline (extra-) mixing, which is more effective for metal-poor RR Lyrae stars. This is clearly seen in the plot showing that C/N ration in our sample of stars gradually decreases as metallicity decreases from about −0.2 to −2. Oxygen abundance depends on metallicity in a similar way to what we see in the Population II stars.

中文翻译：

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九个野外 RR Lyr 型恒星样本中的 NLTE CNO 丰度

首次对九颗天琴座RR星的光谱中的碳和氮谱线进行了直接非局域热力学平衡（NLTE）分析。我们已经确定了这些元素与氧的丰度，并表明金属丰度不足的程序恒星中的氮含量增加。我们得出结论，这是第一次疏浚的迹象，它发生在红巨星分支的前一阶段，并将经过不完全碳、氮、氧 (CNO) 循环处理的物质带到了恒星表面。这种效应通过温盐（额外）混合得到显着增强，这对贫金属的天琴座RR星更有效。从图中可以清楚地看出，随着金属丰度从 -0.2 降低到 -2，我们恒星样本中的 C/N 比逐渐降低。