Evolutionary sequences of stellar models with semiconvection and convective overshoot. I. Z=0.008.

We present two grids of evolutionary stellar models covering the phases of core H- and He-burning for stars having masses in the range 0.6M. to 100M. with composition (Y = 0.25 and Z = 0.008). The computations were performed for two different mixing schemes in the convective regions, i.e. either the classical definition of the convective core during the central H-burning phase and semiconvection during the core He-burning phase or non local overshoot from convective regions all over the major nuclear phases. All the evolutionary models were computed from the main sequence up to the stage of central carbon ignition or to the beginning of the thermally pulsing regime of the asymptotic giant branch phase as appropriate to the value of the initial stellar mass. Massive stars (M greater-than-or-equal-to 12M.) were evolved considering the effect of mass loss by stellar wind, whereas low and intermediate mass stars were calculated at constant mass. For these latter, mass loss during the red giant and asymptotic giant branch phases can be easily included following the standard analytical procedure. Care was paid to upgrade the physical input of the numerical code, i.e. nuclear reaction rates and accompanying nucleosynthesis network (16 elements were actually followed), opacities, neutrino energy losses, boundary conditions in the outer layers, and mass loss rates for massive stars. The results are presented in tabular form giving as much information as possible. Finally, we concisely compare the main characteristics of the evolutionary models obtained with the two mixing schemes