Vol 22, No 3

Evaluating Helium Variations By Modeling Red Giant Branch Bump of Large Magellanic Cluster NGC 1978

Xin Ji, Cheng-Yuan Li, Li-Cai Deng


Abstract Many evidences show that the Multiple Population (MP) features exist not only in old clusters but also in intermediate-age clusters in the Megallanic Clouds (MCs), which are characterized by star-to-star abundance scatter of several elements, including helium (He). The red giant branch bump (RGBB)ʼs photometric properties are proved to be related to the variation in helium abundances of the member stars in star clusters. We use the “Modules for Experiments in Stellar Astrophysics” (MESA) stellar evolution code to calculate the evolution sequences of stars along the red giant branch (RGB) with changing helium content. Following the RGB sequences, we then generate a luminosity function of the RGB stars within the grid of input helium abundances, which are compared with the observational data of an intermediate-age MC cluster NGC 1978.


Keywords globular clusters: general – globular clusters: individual (NGC 1978) – stars: abundances – stars: Hertzsprung–Russell and C–M diagrams – stars: luminosity function

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