Effects of α-Enhancement on Stellar Evolution

Using Eggleton's code, we systematically show the differences in stellar evolution between the results based on the scaled-solar mixture and the a-enhanced metal mixture. As input, the OPAL high temperature opacities are used for log(T/K) > 4.00, and the new Wichita State low temperature opacities, for log(T/K) <= 4.00. Our calculations cover star masses ranging from 0.25 to 80.0 M(circle dot), spaced at Delta log M = 0.10 or 0.05. The values of metallicities Z are 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08 and 0.10. For a given Z, the initial hydrogen mass fraction is given by X = 0.76 - 3.0Z. We show that alpha-enhancement can raise the stellar effective temperature and luminosity, and reduce the evolutionary age. Compared with some previous work, the effects of alpha-enhancement are more obviously demonstrated in our calculations.