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We evaluated the bias and variability on the fitted age and convective coreovershooting parameter for evolved binary stars accounting for observationaland internal uncertainties. We considered a binary system composed of a 2.50$M_{\sun}$ primary star coupled with a 2.38 $M_{\sun}$ secondary in threeevolutionary stages (primary at the end of the central helium burning; at thebottom of the RGB; and in the helium core burning). The simulations have beencarried out for two values of accuracy on the mass determination (1% and 0.1%).We found that the fitted age and overshooting efficiency are always biasedtowards low values. The underestimation is relevant for a primary in thecentral helium burning stage, reaching -8.5% in age and -0.04 (-25% relativeerror) in the overshooting parameter $\beta$. In the other scenarios, anundervaluation of the age by about 4% occurs. A large variability in the fittedvalues between simulations was found: for an individual system calibration, thevalue of $\beta$ can vary from 0.0 to 0.26. For an error of 0.1% on the massesthe global variability is suppressed by a factor of two. We accounted for asystematic offset in the effective temperature of the stars by $\pm 150$ K. Fora mass error of 1% $\beta$ is largely biased towards the edges of the exploredrange, while for the lower mass uncertainty it is basically unconstrained from0.0 to 0.2. We evaluated the possibility of individually recovering the $\beta$value for both stars. We found that this is impossible for a primary near tocentral hydrogen exhaustion, while in the other cases the fitted $\beta$ areconsistent, but always biased. Finally, the possibility to distinguish betweenmodels computed with mild overshooting from models with no overshootingresulted in a reassuring power of 80%. However, the scenario with a primary inthe central helium burning showed a power lower than 5%.

Overshooting calibration and age determination from evolved binary system