A comparison of stellar evolution with binary systems

We have compared stellar evolution models with the three intermediate-mass binary systems V2291 Oph, α Aur, and η And, whose masses are determined accurately within 7%. These systems were recently regarded by Schröder and coworkers as systems that favor evolution with moderate overshoot mixing from the convective cores. While they assumed a standard Population I metallicity for these binaries, we have taken into account the available heavy-element abundance data in the literature. We have taken two approaches for each system. First, assuming no core overshooting, we have adjusted helium abundance for each binary to obtain the best fit. Second, adopting a helium abundance from a standard metallicity-helium relation, we have estimated a required extent of core overshooting l_ov. Our results indicate that the required extent of core overshooting is less than ∼0.15H_p, which is smaller than the extent estimated by Schröder and his collaborators. The main reason for the difference is attributed to the fact that we have taken into account published estimates of metallicity for each system. We have found that to obtain a good fit with red components we have to modify the ratio of mixing length to pressure scale height for each system. The required ratio is found to be smaller for a metal-poor system and vice versa.