Evolutionary tracks and isochrones for alpha-enhanced stars

We present four large sets of evolutionary tracks for stars with initial ch emical compositions [Y = 0.250, Z = 0.008], [Y = 0.273, Z = 0.019], [Y = 0. 320, Z = 0.040] and [Y = 0.390, Z = 0.070] and enhancement of ct elements w ith respect to the solar pattern. The major improvement with respect to pre vious similar calculations is that we use consistent opacities - i.e. compu ted with the same chemical composition as adopted in the stellar models - o ver the whole relevant range of temperatures. For the same initial chemical compositions [Y, Z] and otherwise identical input physics we present also new evolutionary sequences with solar-scaled mixtures of abundances. Based on these stellar models we calculate the corresponding sets of isochrones b oth in the Johnson-Cousins U BV RI J H K and HST/WFPC2 photometric systems. Furthermore, we derive integrated magnitudes, colours and mass-to-light ra tios for ideal single stellar populations with total mass equal to 1 M-circ le dot. Finally, the major changes in the tracks, isochrones, and integrate d magnitudes and colours passing from solar-scaled to alpha -enhancedmixtur es are briefly outlined. Retrieval of the complete data set is possible via the www page http://pleiadi.pd.astro.it.