Old open clusters as key tracers of Galactic chemical evolution

Abstract

Aims. To constrain the formation and chemical evolution of the Galactic disk, we surveyed open clusters of different ages, metal contents, and distances from the Galactic centre. We employed FLAMES on VLT-UT2 to collect UVES spectra of five to ten giant stars in each of the selected clusters and used them to derive the iron abundance and the detailed chemical composition. Methods. Equivalent widths were measured and abundance analysis was performed using the MOOG code and Kurucz model atmospheres on all stars considered as cluster members on the basis of their radial velocity. Results. We derived the atmospheric parameters and the Fe abundance for NGC 2324 and NGC 2477 (average [Fe/H] = -0.17 with rms 0.05 dex, and +0.07 with rms 0.03 dex, respectively), two clusters never analyzed using high resolution spectra. We also derived the abundances of Mg, Al, Ca, Si, Ti, Cr, Ni, and Ba for these two clusters and for NGC 2660, NGC 3960, and Berkeley 32, whose atmospheric parameters and metallicities were measured in a previous paper. We determined the reddening values for the five clusters, based on the spectroscopic temperatures, literature photometry, and a colour-temperature relation. Conclusions. All clusters show solar-scaled abundances for α- and Fe-peak elements, while [Na/Fe] appears slightly enhanced and [Ba/Fe] significantly enhanced. Our findings were compared to thin-disk stars and other open clusters, and no significant deviation from the standard behavior was found.