Effects of triple-α and ¹²C(α, γ)¹⁶O reaction rates on the supernova nucleosynthesis in a massive star of 25 M_O

We investigate the effects of triple-α and ¹²C(α, γ) ¹⁶O reaction rates on the production of supernova yields for a massive star of 25 M_O. We combine the reaction rates to examine the rate dependence, where the rates are considered to cover the possible variation of the rates based on experiments on the earth and on theory. We adopt four combinations of the reaction rates from two triple-α reaction rates and two ¹²C(α, γ) ¹⁶O ones. First,we examine the evolution ofmassive stars of 20 M_O and 25 M_O whose helium cores correspond to helium stars of 6 M_O and 8 M_O, respectively. While the 25 M_O stars evolve to the presupernova stages for all combinations of the reaction rates, the evolutionary paths of the 20 M_O stars proceed significantly differently for some combinations, which are unacceptable for progenitors of supernovae. Second, we perform calculations of supernova explosions within the limitation of spherical symmetry and compare the calculated abundance ratios with solar system abundances. We can deduce some constraints to the reaction rates. The results show that a conventional rate is adequate for a triple-α reaction rate and a rather higher value of the reaction rate within the upper limit for the experimental uncertainties is favorable for a ¹²C(α, γ) ¹⁶O rate.