THE EFFECT OF CORE OVERSHOOTING AND MASS-LOSS ON THE INTERNAL DENSITY CONCENTRATION OF MAIN-SEQUENCE STARS

A comparative study between standard evolutionary models and those which take into account core overshooting and mass loss is presented concerning the internal density concentration of main sequence stars. Three models, with 2.5, 10 and 25 solar masses, were used for this study in order to cover the mass range where observations of apsidal motion parameters are available. We have found that models with non-standard physics are more centrally concentrated in mass than the standard ones for the same stellar mass and radius. The observational fact that the more evolved systems present also the greatest discrepancies in the log k2 - log g plane with respect to theoretical predictions using standard models is also shown by the present calculations to be the case for non-standard models with respect to standard computations. Furthermore, we have found that for binary systems whose surface parameters are equally well reproduced by standard and non-standard evolutionary models, the discrepancies between observation and theory in log k2 are significantly decreased taking into account core overshooting. Five binary systems at different stages of evolution, were studied in order to estimate quantitatively the still remaining discrepancies between theoretical predictions and observational results for the internal structure constants, when the influence of overshooting in the core is considered. Unfortunately a physically realistic amount of overshooting and/or mass loss did not fully explain the observed differences in log k2 though the general picture clearly improves.