Stellar population synthesis revisited

The isochrone synthesis method is introduced as a population synthesis method for galaxies. The method permits accurate distributions of stars in the theoretical color-magnitude diagram to be computed for any stellar population and thereby circumvent the problems faced by earlier techniques. A set of evolutionary tracks extending from the ZAMS up to the beginning of the white-dwarf cooling sequence is compiled to optimize the models. Comparison of model predictions with observational data leads to the conclusion that the isochrone synthesis can reproduce the observed colors of stellar populations of ages from a few tens of millions of yr to a Hubble time.