THE ASTRONOMICAL JOURNAL    VOLUME 109, NUMBER 1, PAGE 269         JANUARY 1995

              BVI CCD PHOTOMETRY OF NGC 5053: THE MOST METAL-POOR
                           GALACTIC GLOBULAR CLUSTER

                                ATA SARAJEDINI

   Kitt Peak National Observatory, National Optical Astronomy Observatories,
                     P.O. Box 26732, Tucson, Arizona 85726
                         Electronic mail: ata@noao.edu

                            ALEJANDRA A. E. MILONE

        Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,
                        Cambridge, Massachusetts 02138
                    Electronic mail: milone@cfa.harvard.edu


                                   ABSTRACT
    
    We present (V,B-V), (V,V-I), and (V,B-I) color-magnitude diagrams for
    NGC 5053, which is the most metal-poor globular cluster known in the
    galaxy.  The horizontal branch (HB) is predominantly blueward of the RR
    Lyrae instability strip and the slope of the red giant branch (RGB) is
    relatively steep, both characteristic of a metal-poor system.  Monte-
    Carlo simulations show that both the RGB and HB are underpopulated
    relative to those of the metal-poor cluster M15, indicative of the
    relatively lower total luminosity of NGC 5053.  Based on the mean
    magnitude of stars located at the red and blue edges of the instability
    strip, we find V(HB) = 16.65 +/- 0.03.  At this magnitude, polynomial
    fits to the cluster RGBs in the two measured colors yield (B-V)_g =
    0.71 +/- 0.016 and (V-I)_g = 0.93 +/- 0.016.  Using the BVI two-color
    diagram in a differential manner with respect to M68 and M15 gives a
    reddening of E(B-V) = 0.06 +/- 0.02 for NGC 5053.  We have utilized
    these quantities to extend the calibration of the simultaneous
    reddening and metallicity method [Sarajedini, AJ, 107, 618 (1994a)] to
    [Fe/H] = -2.4.  Another feature of the color-magnitude diagram that is
    evident is the rich population of blue straggler stars (BSSs). We are
    able to recover 22 of 24 previously known BSSs, and we have added 3
    more BSSs.