论文标题
RR Lyrae变量的表面C，N，O和Na丰度，暗示着低质量星体内部混合的性质
Surface C, N, O, and Na abundances of RR Lyrae variables implying the nature of internal mixing in low-mass stars
论文作者
论文摘要
通过将合成频谱拟合技术应用于34个快照射击的高散位光谱，确定了C，N，O和Na的光球丰度，该技术覆盖了22 RR Lyr恒星，涵盖了-1.8 <[fe/h] <0.0的金属性范围，该金属性范围为-1.8 <[fe/h] <0.0 <0.0，目的是通过调查较低的元素中的混合机制，以这些元素进行这些元素，以这些元素的范围内的混合机制，以这些元素进行这些元素，以这些元素的范围内的元素进行了这些元素，这些元素是在这些元素中进行的，这些元素的含量是在这些元素中，这些元素的含量是在这些元素中的范围，这些元素是在这些元素中的融合机制进化引起的核燃烧产品的挖掘。特别注意检查最近的理论恒星进化模拟，表明热盐混合在低质量恒星中的重要性（M <〜1 m_sun），随着金属性的降低，预计会更重要。通过检查所得的丰度与未发展的金属贫困矮人相同的金属性相比，确认了C的缺乏以及N中的富集（而O几乎没有变化），而[Fe/H]的特殊性程度趋于增加。因此，[c/n]比率逐渐降低了金属性，从〜0（fe/h] 〜0）降至〜-1（[fe/h]〜-1.5），这与在嗜热盐混合的情况下在理论预测中相当一致。然而，尽管对于非统一混音，但这些RR ly恒星并未表现出任何明显的Na异常（即与[na/fe]与[Fe/H]趋势相同的[Fe/H]趋势），尽管Na在Na中依赖于Na中的金属依赖性过高。 C/N和NA之间的这种不一致可能表明需要进一步改善当前理论。
Photospheric abundances of C, N, O, and Na were determined by applying the synthetic spectrum-fitting technique to 34 snap-shot high-dispersion spectra of 22 RR Lyr stars covering a metallicity range of -1.8 <[Fe/H] < 0.0, with an aim of investigating the mixing mechanism in the interior of low-mass giant stars by examining the abundance anomalies of these elements possibly affected by the evolution-induced dredge-up of nuclear burning products. Special attention was paid to check the recent theoretical stellar evolution simulations indicating the importance of thermohaline mixing in low-mass stars (M <~1 M_sun), which is expected to be more significant as the metallicity is lowered. By inspecting the resulting abundances in comparison with those of unevolved metal-poor dwarfs at the same metallicity, the deficiency in C as well as enrichment in N was confirmed (while O is almost unchanged), the extent of peculiarities tending to increase with a decrease in [Fe/H]. Accordingly, the [C/N] ratio turned out to progressively decrease towards lower metallicity from ~0 (Fe/H]~0) to ~-1 ([Fe/H]~-1.5), which is reasonably consistent with the theoretical prediction in the presence of thermohaline mixing. However, these RR Lyr stars do not show any apparent Na anomaly (i.e., essentially the same [Na/Fe] vs. [Fe/H] trends as those of dwarfs), despite that metallicity-dependent overabundance in Na is theoretically expected for the case of non-canonical mixing. This inconsistency between C/N and Na may suggest a necessity of further improvement in the current theory.
