论文标题
当地组星系中AGB星的C/M比
The C/M Ratio of AGB Stars in the Local Group Galaxies
论文作者
论文摘要
富含碳与富氧的渐近巨型分支（AGB）恒星（所谓的C/M比）的数量比与宿主星系的进化环境密切相关。这项工作研究了本地组中14个星系中的C/M比，其中最完整，最干净的成员恒星样本在我们以前的作品中鉴定出来。高斯混合模型在$（J-k）/k $图中的数量密度拟合，为LMC和M33的成员明星拟合的高斯混合模型定义了富含碳和富含氧气的AGB的邻缘和红色超级巨星之间的边界线，然后通过将其用于其他星系的差异来迁移到其他星系的差异。 C/M比在精确且一致的分类后获得。尽管对于具有较大距离模量的星系存在更大的不确定性，但C/M比清楚地发现TRGB的颜色指数$（J -K）_0 $作为金属性指标，这与先前的研究相一致，并且可以通过以下事实来解释，即在金属量环境中更容易形成碳星。此外，发现M33内的C/M比随着半乳酸距离而增加，这与这种情况和银河化学演化模型相吻合。另一方面，发现M31内的C/M比随着半半径的半径而降低，这值得进一步研究。
The number ratio of carbon-rich to oxygen-rich asymptotic giant branch (AGB) stars (the so-called C/M ratio) is closely related to the evolution environment of the host 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 identified in our previous works. The borderlines between carbon-rich AGB and oxygen-rich AGB stars as well as red supergiants are defined by Gaussian mixture model fitting to the number density in the $(J - K)/K$ diagram for the member stars of the LMC and M33, and 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 precise and consistent categorization. Although for galaxies with larger distance modulo there is greater uncertainty, the C/M ratio is clearly 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 the fact that carbon stars are more easily formed in a metal-poor environment. Furthermore, the C/M ratio within M33 is found to increase with galactocentric distance, which coincides with this scenario and the galactic chemical evolution model. On the other hand, the C/M ratio within M31 is found to decrease with galactocentric radius, which deserves further study.
