御夫座α星碳12 C/13 C同位素比值的修正
Carbon 12C/13C isotope ratio of alpha Aurigae revised
摘要：
上下文五车二（α Aur）是天空中为数不多的拥有两颗冷巨星的双星之一。光谱类型为G8 III和G 0 III，这两种成分在其演化过程中出现在不同但截然不同的阶段。G 0的副恒星是一颗赫兹波隙巨星，而G8的主星则被认为是一颗团巨星。目的。我们提出了一个新的测量的碳12 C/ 13 C同位素比率的主要组成部分五车二使用高分辨率R $\approx$ 250 000光谱获得的波茨坦Echelle偏振和光谱仪器（PEPSI）与梵蒂冈先进技术望远镜（VATT）和大双筒望远镜（LBT）。方法.通过对夜间光谱进行平均，获得了高达2 700的信噪比。这些平均光谱用于解开两个二元组分。同位素比是利用8004度的CN线的光谱合成得到的。结果我们发现五车二主要成分的12 C/ 13 C比值为17.8 $\pm$ 1.9。我们的测量精度现在主要受到谱线数据和模型大气的网格步长的限制，而不是数据。第二组分的分离光谱由于其vsin i和较高的温度而不显示可区分的12 CN和13 CN线。结论.我们新的12 C/ 13 C值明显低于以前的值27 $\pm$ 4，但现在与最近的模型预测18.8 - 20.7更好地吻合。
英文摘要：
Context. Capella (α Aur) is one of the few binaries in the sky with two cool giant stars. With spectral types of G8III and G0III, the two components appear at different but distinct stages in their evolution. The G0 secondary star is a Hertzsprung-gap giant, and the G8 primary star is thought to be a clump giant. Aims. We present a new measure of the carbon 12 C/ 13 C isotope ratio of the primary component of Capella using high-resolution R $\approx$250 000 spectra obtained with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) with both the Vatican Advanced Technology Telescope (VATT) and the Large Binocular Telescope (LBT). Methods. Signal-to-noise ratios of up to 2 700 were obtained by averaging nightly spectra. These average spectra were used to disentangle the two binary components. The isotope ratio was derived with the use of spectrum synthesis from the CN lines at 8004 Å. Results. We found that the 12 C/ 13 C ratio of the primary component of Capella is 17.8$\pm$1.9. Our measurement precision is now primarily limited by the spectral-line data and by the grid-step size of the model atmospheres rather than the data. The separated spectrum of the secondary component does not show distinguishable 12 CN and 13 CN lines because of its v sin i and higher temperature. Conclusions. Our new 12 C/ 13 C value is significantly lower than the previous value of 27$\pm$4 but now agrees better with the recent model prediction of 18.8 - 20.7.
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