THE ASTRONOMICAL JOURNAL    VOLUME 107, NUMBER 1, PAGE 230          JANUARY 1994

          BVRI CCD PHOTOMETRY OF THE GLOBULAR CLUSTER NGC 1904 (M79)

    GONZALO ALCAINO, WILLIAM LILLER, FRANKLIN ALVARADO, AND ERICH WENDEROTH

           Instituto Isaac Newton, Ministerio de Educacion de Chile,
                    Casilla 8-9, Correo 9, Santiago, Chile
 

                                   ABSTRACT

    We present BVRI photometry of three overlapping fields in the globular
    cluster NGC 1904 (M79), observed with a CCD camera and the 2.2 m
    Max-Planck-Institute telescope at ESO/La Silla.  We critically compare
    our photometry using the INVENTORY data reduction code with results
    derived by other investigators using different codes.  These
    comparisons convince us that all modern codes give results reliable to
    at least +/- 0.3 mag at all levels, as long as the fields are not
    overly crowded.  Specifically, our results for NGC 1904 (M79) are as
    follows: V(TO) = 19.60 +/- 0.10 (estimated external error), with
    turnoff colors at B-V = 0.40, V-R = 0.27, V-I = 0.57, and B-I = 0.97,
    all with estimated external errors of +/- 0.06.  By fitting the four
    resulting ridge lines to the theoretical isochrones of VandenBerg &
    Bell [ApJS, 58, 561 (1985)] interpolated to [Fe/H] = -1.60, Y = 0.20,
    and [O/Fe] = 0.00, we derive an average value for the age of 16 Gyr,
    where we have adopted E(B-V) = 0.01.