Evolution of Massive Stars. II Helium-Burning Stage

To investigate the evolution of massive stars in the helium-burning stage, four sample models (M = 15.6M_⊙) consisting of the following four regions are constructed: (1) hydrogen-rich envelope, (2) radiative zone with varying hydrogen content, (3) radiative helium region, (4) convective helium core. The results show that these models lie in the Hertzsprung gap of the h and χ Persei cluster and do not explain the existence of the red supergiants branch of this cluster. These models are also compared with those in which the rate of helium burning is slower by a factor of 10. The comparison shows that the properties of models having the double energy-source are very sensitive to the rates of both the hydrogen- and helium-burning.