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.
KeywordsBurning Convection Helium 2oNe Agram
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