Involved people at OAB: Bonifazi, Bragaglia, Tosi.
Open clusters (OC's) are ideal objects to trace the Galactic disk: they are found in all disk regions, cover a large interval in age (from a few million years to about 10 Gyr) and in metallicity ([Fe/H] from -1 to more than solar). Hence, they are excellent tools to understand the evolution of our Galaxy from both the chemical and structural points of view, also because OC's are perhaps the only disk objects whose ages and metallicities can be precisely measured (Bragaglia et al. 2000a,b).
As an example of the importance of OC's we may look at the history of the Galactic chemical evolution: many of the existing models are able to reproduce rather well the present-day situation, but differ significantly (Tosi 2000a) in the "history" of the chemical enrichment (hence in the involved processes). In particular, they differ in the predictions for the evolution of the abundance gradients: does the gradient slope steepen or flatten with time? From the OC's we can extract fundamental information, since they can be used to describe the run of the various elemental abundances at different ages.
In order to study in more detail the metallicity and age distribution with galactocentric distance, we are analyzing with great accuracy a sample of open clusters at various galactic locations and covering a wide range in age and metallicity. Our goal is to study at least 30 OC's covering a wide range in the observed properties. Age, distance modulus, reddening and approximate metallicity of the clusters are derived from their Color-Magnitude Diagrams (CMDs) using the synthetic CMD technique and further constrained by the observed luminosity functions. It must be emphasized that this analysis requires a high degree of homogeneity, since the use of literature values can lead to a confusing picture: e.g. ages, derived with different techniques/isochrones, may not only be uncertain in absolute value, but also in ranking. Precise and homogeneous elemental abundances are determined from high resolution spectroscopy; note that only about 18 of the about 80 old OC's have ever been studied with high resolution spectroscopy, and only a handful have abundances of elements other than iron. This research is in collaboration with Marconi (OAR), Carretta and Gratton (OAPd).
So far we have studied in detail the CMDs of about 10 OC's (NGC7790, NGC4815, IC1311, NGC2660, NGC2506, Be21, NGC6253, NGC2243, Cr261) and have acquired photometric data for 10 more using various telescopes (Dutch, Danish, and NTT in La Silla; Loiano; TNG). During 1999, we have completed the study of NGC2660 (Sandrelli et al. 1999). In addition, photometric data (on Be29 and Be17) have been acquired at the TNG and high-res spectroscopic data (on NGC4815, NGC2506, NGC6253 and Cr261) at NTT.