1998/12/15 by G. Carraro, Giovanni Carraro, Carraro, Giovanni +9
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics (astro-ph) #Astrophysics and Star Formation Studies #FOS: Physical sciences #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9812278
8 pages, 6 figures, to appear in Astronomy and Astrophysics Main Sequence
arxiv created 1998/12/15 · openalex publication_date 1998/12/15 · arxiv updated 2009/12/01 · openalex created_date 2022/10/03 · openalex updated_date 2026/07/28
We report on near IR (J and K bands) observations of two 8 \× 8\n ~(arcmin)2 regions centered on the old open clusters Berkeley~17 and\nBerkeley~18, for which only optical photometry (in B,V and I bands)\nexists. J and K photometry allows us to obtain an independent estimate of\ncluster metallicity by means of the relationship between the spectroscopic\nmetallicity and the Red Giant Branch (RGB) slope calibrated by Tiede et al\n(1997). From the analysis of the colour magnitude diagram (CMD) and luminosity\nfunction (LF), Berkeley~17 turns out to have a metal content\n[Fe/H]~\∼~-0.35. It is 9~Gyr old, suffers from a reddening E(B-V) = 0.58\nmag and has an heliocentric distance of 2.5 kpc. Berkeley~17 comes out to be\nsubstantially younger than in previous work (age \≈ 13~Gyr). On the\nother hand Berkeley~18 is found to have solar metal abundance, and to be\nyounger than Berkeley~17, with an age of about 4~Gyr. While we confirm\nKaluzny (1997) reddening estimate, we significantly revise the distance of the\ncluster, which lies 4.5 kpc from the Sun. These results on two open clusters\nbelieved to be between the oldest put constraints on the age and the evolution\nof the Galactic Disc. The absence of clusters older than 8-9~Gyr suggests the\npossibility that the Galaxy underwent a star formation minimum between 13 and\n10~Gyr ago.\n