Study On The Color-magnitude Diagrams Of 12 Globular Clusters In The Galaxy

The Galactic globular cluster is composed of old stars,with high density of central stars and spherical or ellipsoidal appearance.It plays an important role in the formation of celestial environment and the ionization of molecular clouds in the early stage of the Milky Way.The traditional globular cluster model considers that the stars in the cluster form once in the molecular cloud,and the metal abundance,age,moving direction and velocity of the member stars are almost the same.More and more observations show that there are binary star,multiple population and special stars in globular clusters,which is quite different from the traditional globular cluster model.In order to improve the formation and evolution model of globular clusters,and quantify the influences of different stellar population models,we use the Advance Stellar Population Synthesis(ASPS)model to study the colormagnitude diagrams of 12 globular clusters in the Galaxy.First of all,I chose 12 galactic globular clusters provided by the Hubble Space Telescopes UV globular cluster survey(" HUGS")as my research objects.Through the data processing of F606W(V-band)and F438W(B-band)of globular clusters,the observation error and influence of field stars are reduced,and the color-magnitude diagrams of 12 globular clusters is constructed.Then we use three kinds of stellar population models in the ASPS model: single star simple stellar population model,binary star simple stellar population model and binary star composite stellar population model to study their color-magnitude diagrams,and analyze the determination of parameters,the reproduction of color-magnitude diagrams,the proportion of blue stragglers and the distribution of stars in color and magnitude frequency via different stellar population models.The new age and metallicity of NGC 6652,NGC 6637 and NGC 4833 are given,which can be used in the future study of various clusters.The results show that:(1)The binary star and its evolution are very important in the study of the color-magnitude diagram of the globular clusters,because it can reproduce more observation phenomena,e.g.the main sequence broadening,blue stragglers and red stragglers;(2)The best parameters of globular clusters determined in this work are roughly the same as those in Harris catalog literature,and the age determined is more accurate and more consistent with the theoretical age of galactic globular clusters than Dotter et al.(2010),which can provide reference for further research work in the future;(3)Through quantitative analysis of the proportion of blue stragglers in observation and the binary star simple stellar population model,our results and data support that the evolution of binary star is the main cause of forming blue stragglers rather than star collision;(4)After analyzing the frequency distribution of stars in color and magnitude,it is found that the binary star stellar population model is closer to the observed color frequency distribution than the single star stellar population model,which means that binary star and their evolution will affect the evolution of the stellar population in the globular cluster;(5)Compared with the simple stellar population model,the composite stellar population model is closer to the frequency distribution of stars in color,especially the trend of color frequency distribution near the turn-off point.Finally,our understanding of the problem of multiple stellar population in globular clusters is proposed.