A comparison is made between the age–metallicity relations obtained from four different types of studies: F and G stars in the solar neighbourhood, analysis of open clusters, galactic structure studies with the stellar population synthesis technique and chemical evolution models. Metallicities of open clusters are corrected for the effects of the radial gradient, which we find to be −0.09 dex kpc−1 and most likely constant in time. We do not correct for the vertical gradient, because its existence and value are not firmly established. Stars and clusters trace a similar age–metallicity relation, showing an excess of rather metal‐rich objects in the age range 5–9 Gyr. Galactic structure studies tend to give a more metal‐poor relation than chemical evolution models. Neither relation explains the presence of old, relatively metal‐rich stars and clusters. This might be caused by uncertainties in the ages of the local stars, or pre‐enrichment of the disc with material from the bulge, possibly as a result of a merger event in the early phases of the formation of our Galaxy.

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Abstract.A new method, AMORE -based on a genetic algorithm optimizer, is presented for the automated study of colourmagnitude diagrams. The method combines several stellar population synthesis tools developed in the last decade by or in collaboration with the Padova group. Our method is able to recover, within the uncertainties, the parameters -distance, extinction, age, metallicity, index of a power-law initial mass function and the index of an exponential star formation rate -from a reference synthetic stellar population. No a priori information is inserted to recover the parameters, which is done simultaneously and not one at a time. Examples are given to demonstrate and to better understand biases in the results, if one of the input parameters is deliberately set fixed to a non-optimum value.

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Abstract. A quantitative method is presented to compare observed and synthetic colour-magnitude diagrams (CMDs). The method is based on a χ 2 merit function for a point (c i , m i ) in the observed CMD, which has a corresponding point in the simulated CMD within nσ(c i , m i ) of the error ellipse. The χ 2 merit function is then combined with the Poisson merit function of the points for which no corresponding point was found within the nσ(c i , m i ) error ellipse boundary.Monte-Carlo simulations are presented to demonstrate the diagnostics obtained from the combined (χ 2 , Poisson) merit function through variation of different parameters in the stellar population synthesis tool. The simulations indicate that the merit function can potentially be used to reveal information about the initial mass function. Information about the star formation history of single stellar aggregates, such as open or globular clusters and possibly dwarf galaxies with a dominating stellar population, might not be reliable if one is dealing with a relatively small age range.