渐近巨星支星(AGB星)是演化阶段末期的中小质量恒星，具有明显的红外辐射。其强烈的对流过程将恒星内部的核合成产物挖掘到表面，大气的碳元素丰度增加，直至形成碳丰度高于氧的富碳AGB星。富碳AGB星与富氧AGB星的数量比被称为C/M比，它可揭示星系中星族的演化环境。基于完备而纯净的成员星星表，本项工作研究了本星系群内14个星系中AGB星的C/M比。富碳或富氧的AGB星以及红超巨星之间的边界，是通过对LMC和M33两个基准星系中的成员星的(J?K)0/K0图中的数量密度借助高斯混合模型分析确定的。根据红巨星支顶端(TRGB)的位置差异将基准星系的边界线应用于其他星系以进行分类，得到了各星系的C/M比。C/M比被发现随着TRGB的色指数(J?K)0这一金属丰度的指标的降低而增加，这与以前的研究一致，可以解释为碳星在贫金属的环境中更容易形成。M33内的C/M比被发现随着星系中心距离的增加而增加，这也与星系化学演化模型相吻合。然而，M31中的C/M比却被发现随着星系中心距离的增加而降低，这需要进一步的研究。此外，对富碳AGB星作为替代性的标准烛光的效果也进行了初步检验。

Asymptotic giant branch stars (AGB stars) are low- to intermediate mass stars at the end of their evolutionary stage with intense infrared flux. Their strong convection transfer the nucleosynthesis products from the interior to the surface, and the abundance of carbon in the atmosphere increases, forming carbon-rich AGB stars whose atmosphere consists of more carbon than oxygen. The number ratio of carbon-rich to oxygen-rich asymptotic giant branch (AGB) stars (C/M ratio) reveals the evolution environment of a galaxy. This work studies the C/M ratio in 14 galaxies within the Local Group with the most complete and clean sample of member stars. The borderlines between C-AGB and O-AGB stars as well as red supergiants are defined by Gaussian mixture model to the number density in the (J ? K)0/K0 diagram for the member stars of two benchmark galaxies, LMC and M33. The borders are then applied to the other galaxies by shifting the difference in the position of tip red giant branch (TRGB). The C/M ratios are obtained after the categorization. The C/M ratio is found to decrease with the color index (J ? K)0 of TRGB as the indicator of metallicity, which agrees with previous studies and can be explained by that car- bon stars are more easily formed in metal-poor environment. The C/M ratio within M33 is found to increase with galactocentric distance, which also coincides with this scenario and the galactic chemical evolution model. However, the C/M ratio in M31 is found to decrease with galactocentric radius, which deserves further study. In addition, the effectiveness of C-AGB stars as alternative standard candles is preliminarily tested.