The C/M Ratio of AGB Stars in the Local Group Galaxies

The number ratio of carbon-rich to oxygen-rich asymptotic giant branch (AGB) stars (the so-called C/M ratio) is closely related the evolution environment host galaxy. This work studies in 14 galaxies within Local Group with most complete and clean sample member identified our previous works. borderlines between AGB as well red supergiants are defined by Gaussian mixture model fitting density (J−K)/K diagram for LMC M33, then applied other shifting difference position tip (TRGB). ratios obtained after precise consistent categorization. Although larger distance modulo there greater uncertainty, clearly found decrease color index (J−K)0 TRGB indicator metallicity, which agrees can be explained fact that carbon more easily formed a metal-poor environment. Furthermore, M33 increase galactocentric distance, coincides this scenario galactic chemical model. On hand, M31 radius, deserves further study.