THE ASTROPHYSICAL JOURNAL, 483:826, 1997 July 10

                     BERKELEY 17: THE OLDEST OPEN CLUSTER?

                                RANDY L. PHELPS
           Observatories of the Carnegie Institution of Washington,
         813 Santa Barbara Street, Pasadena, CA 91101; phelps@ociw.edu


                                   ABSTRACT

        Faint magnitude BVI CCD photometry of the central region of the old
     open cluster Berkeley 17 (Be 17) has been undertaken to investigate
     the claim that it is the oldest open cluster yet discovered (Phelps,
     Janes, & Montgomery). This study reveals Be 17 to have a metallicity
     -0.30 <= [Fe/H] <= 0.00; a reddening 0.52 <= E(B-V) <= 0.68 or 0.61 <=
     E(V-I) <= 0.71; a distance modulus, (m-M)0 = 12.15 +/- 0.10,
     corresponding to a distance of 2.7 +/- 0.1 kpc; a diameter of ~10 pc;
     a minimum mass of 400 Msun; and an age of 10-13 Gyr.  With an adopted
     age of 12(+1)(-2) Gyr, these results suggest that Be 17 is indeed the
     oldest open cluster yet discovered. The inferred old age for Be 17
     indicates that the cluster is an important one for studies of the
     differences between open and globular clusters, the transition from
     the halo/thick disk to the thin disk of the Galaxy, and even for
     establishing the minimum age of the universe.


     Subject headings: Hertzsprung-Russell diagram --
                       open clusters and associations: individual
                       (Berkeley 17) -- stars: abundances --
                       stars: evolution