标题： 使用CH带测量恒星中碳丰度的注意事项 显示英文标题

标题： Caveats about measuring carbon abundances in stars using the CH band

摘要： 准确估算各种恒星的碳丰度仍然很复杂，这是由于从原子和分子线中正确测量它存在困难。 本文的目的是分析大型经验X-shooter光谱库（XSL）中的碳丰度测定，该库常用于恒星种群模型的开发作为基准。 分析是在G带区域的强分子CH带进行的。 我们使用了GAUGUIN自动光谱合成代码，并分别采用了两个不同的参考合成光谱网格，每个网格都有相同的[C/Fe]丰度覆盖范围。 我们对这两个网格进行了详细比较，以评估测量的[C/Fe]丰度的准确性和模型依赖性。 我们从两个理论网格中获得了大量且精确的无偏[C/Fe]丰度目录，在赫茨普龙-罗素（HR）图中分布良好，并且没有与恒星参数相关的趋势。 我们还从每个独立的CH带中测得了相容的值，对于矮星和巨星都得到了高质量的[C/Fe]丰度估计。 我们在整个金属丰度范围内观察到围绕[C/Fe] = 0.0 dex的分散平坦趋势，这与一些文献研究一致。 然而，我们报告说，根据所采用的网格，恒星的[C/Fe]组成可能会有高达0.8 dex的变化。 我们在$\alpha$元素测量中没有发现这样的差异。 这种行为意味着[C/Fe]丰度估计具有很强的模型依赖性。 可能的误差来源可能与使用光谱合成方法来推导CH4300A波段中的恒星碳丰度有关。 在这个拥挤和重叠的区域，合成模型之间固有的微小差异可能导致任何恒星类型的精确丰度估计出现很大差异，从而导致不准确的碳测量而未被察觉。 显示英文摘要

摘要： Deriving accurate carbon abundance estimates for a wide variety of stars is still complex due to the difficulties in properly measuring it from atomic and molecular lines. The aim of this paper is to analyse the carbon abundance determination for the large empirical X-shooter Spectral Library (XSL), commonly used as a benchmark for the development of stellar population models. The analysis was performed over strong molecular CH bands in the G-band region. We used the GAUGUIN automated spectrum synthesis code, and adopted two different grids of reference synthetic spectra separately, each with the same [C/Fe] abundance coverage. We carried out a detailed comparison between both grids to evaluate the accuracy and the model dependence of the measured [C/Fe] abundances. We obtained a large and precise unbiased [C/Fe] abundance catalogue from both theoretical grids, well distributed in the Hertzsprung-Russell (HR) diagram and with no trend with the stellar parameters. We also measured compatible values from each independent CH band, with a high-quality [C/Fe] abundance estimate for both dwarfs and giants indistinctly. We observed a dispersed flat trend around [C/Fe] = 0.0 dex all along the metallicity regime, in agreement with some literature studies. However, we reported variations up to 0.8 dex in the [C/Fe] composition of the star depending on the adopted grid. We did not find such differences in the $\alpha$-element measurements. This behaviour implies a strong model dependence in the [C/Fe] abundance estimate. Potential sources of error could be associated with the use of spectral synthesis methods to derive stellar carbon abundances in the CH4300A band. Intrinsic small differences in the synthetic models over this crowded and blended region may induce a large disparity in the precise abundance estimate for any stellar type, leading to inaccurate carbon measurements without being noticed