Scaled solar tracks and isochrones in a large region of the Z-Y plane -: I.: From the ZAMS to the TP-AGB end for 0.15-2.5 M⊙ stars

Context. In many astrophysical contexts, the helium content of stars may differ significantly from those usually assumed in evolutionary calculations. Aims. In order to improve upon this situation, we have computed tracks and isochrones in the range of initial masses 0.15-20 M(circle dot) for a grid of 39 chemical compositions with the metal content Z between 0.0001 and 0.070 and helium content Y between 0.23 and 0.46. Methods. The Padova stellar evolution code has been implemented with updated physics. New synthetic TP-AGB models allow the extension of stellar models and isochrones until the end of the thermal pulses along the AGB. Software tools for the bidimensional interpolation (in Y and Z) of the tracks have been tuned. Results. This first paper presents tracks for low mass stars (from 0.15 to 2.5 M(circle dot)) with scaled-solar abundances and the corresponding isochrones from very old ages down to about 1 Gyr. Conclusions. Tracks and isochrones are made available in tabular form for the adopted grid of chemical compositions in the plane Z-Y. As soon as possible an interactive web interface will allow users to obtain isochrones of any chemical composition and also simulated stellar populations with different Y(Z) helium-to-metal enrichment laws.