The old open cluster Trumpler 5 and the chemical evolution of the galactic disc

Abstract

We present CCD VIKC and Washington CT1 photometry in the field of Trumpler 5. From the comparison of the cluster CMDs with theoretical isochrones, the Standard Giant Branches method and measures of deltaV and deltaT1, we derive reddening, distance, age and metallicity. We examined the overall properties of all clusters with ages of 3 Gyr or older. No evidence either for an abundance Z gradient or for an age-metallicity relation is found. We suggest that the Galactic disc might have been formed inside-out and that the relative lack of very old clusters with Z > 0.5 kpc would be reflecting the transition between the formation of the globular and open cluster systems.