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We present models of alpha Centauri A and B implementing an entropycalibration of the mixing-length parameter alpha_MLT, recently developed andsuccessfully applied to the Sun (Spada et al. 2018, ApJ, 869, 135). In thistechnique the value of alpha_MLT in the 1D stellar evolution code is calibratedto match the adiabatic specific entropy derived from 3D radiation-hydrodynamicssimulations of stellar convective envelopes, whose effective temperature,surface gravity, and metallicity are selected consistently along theevolutionary track. The customary treatment of convection in stellar evolutionmodels relies on a constant, solar-calibrated alpha_MLT. There is, however,mounting evidence that this procedure does not reproduce the observed radii ofcool stars satisfactorily. For instance, modelling alpha Cen A and B requiresan ad-hoc tuning of alpha_MLT to distinct, non-solar values. Theentropy-calibrated models of alpha Cen A and B reproduce their observed radiiwithin 1% (or better) without externally adjusted parameters. The fit is ofcomparable quality to that of models with freely adjusted alpha_MLT for alphaCen B (within 1 sigma), while it is less satisfactory for alpha Cen A (within ~2.5 sigma). This level of accuracy is consistent with the intrinsicuncertainties of the method. Our results demonstrate the capability of theentropy calibration method to produce stellar models with radii accurate within1%. This is especially relevant in characterising exoplanet-host stars andtheir planetary systems accurately.

Testing the entropy calibration of the radii of cool stars: models of alpha Centauri A and B