Old open clusters: the interesting case of Berkeley 21

Abstract

We present CCD BVI photometry of the old open cluster Berkeley 21, one of the most distant clusters in the Galactic anticentre direction, and possibly the lowest metallicity object in the open clusters sample. Its position and metal abundance make it very important for the study of the Galactic disc. Using the synthetic Colour - Magnitude Diagram method, we estimate values for distance modulus (m-M)0=13.4-13.6, reddening E(B-V)=0.74-0.78 (with possible differential absorption), and age=2.2-2.5 Gyr.

13 pages, latex, uses mn.sty, 7 encapsulated figures, to be published in MNRAS, text and figures also available at http://www.bo.astro.it/bap/BAPhome.html or via anonymous ftp at ftp://boas3.bo.astro.it/bap/files (bap98-10-textfig.ps)

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• CCD uvbyHbeta Photometry in Clusters: I. The Open Cluster Standard, IC 4651
• The intermediate age open cluster NGC 2660
• UBVI CCD Photometry of the Old Open Cluster Berkeley 17
• Radial Velocities of Three Poorly Studied Clusters and the Kinematics of Open Clusters
• Multi-Wavelength characterization of VVVX open clusters