About the time of evolution of a solar model

The evolution of a solar model is initialized with homogeneous models of ei ther, pre-main sequence (P-models) or, zero-age main sequence (Z-models). T he zero-age of a solar model is conventionally referenced as the time where the nuclear reactions just begin to dominate gravitation as the primary so urce of energy. Fixing the physics, we found that the structure of P- and Z -models computed with the same physics are almost similar soon after the ex haustion of their convective core. This similarity gives a connection betwe en the age of the Sun t. and the time t(cal) elapsed in the calculation of calibrated solar models. We found that a Z-model calibrated with t(cal) = t . and a P-model calibrated with t(cal) = t. + 25 My, are indistinguishable at the relative accuracy level of a few 10(-4).