Evolution Through Helium Burning — Massive Stars
After central hydrogen burning, the star has a helium core, which in the absence of energy sources tends to become isothermal. Indeed thermal equilibrium would require that the models consist of an isothermal helium core (of mass Mc = qoM, radius Rc), surrounded by a hydrogen-rich envelope [of mass (1 — qo)M] with hydrogen burning in a shell source at its bottom. Such models were discussed in detail in §30.5. We now once more consider the case of M = 3M⊙, which is typical for stars on the upper part of the main sequence (say M > 2.5M⊙). The possible solutions were comprised in a linear series of models consisting of 3 branches. This is shown in the first graph of Fig. 30.10, and again in Fig. 31.1, which also gives the position in the HR diagram.
KeywordsMain Sequence Stellar Mass Linear Series Hydrogen Burning Evolutionary Track
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