Late stages of massive star evolution and nucleosynthesis

The evolution of massive stars in the mass range of 8 - 25 M_⊙ is reviewed. The effect of electron degeneracy on the gravothermal nature of stars is discussed. Depending on the stellar mass, the stars form three types of cores, namely, non-degenerate, semi-degenerate, and strongly degenerate cores. The evolution for these cases is quite distinct from each other and leads to the three different types of final fate. It is suggested that our helium star model, which is equivalent to a 25 M_⊙ star, will fos rm a relatively small mass iron core despite the faster ¹²C (α,γ) ¹⁶O reaction.