THE ASTRONOMICAL JOURNAL      VOLUME 106, NUMBER 2, PAGE 493        AUGUST 1993

        METAL ABUNDANCES FOR A LARGE SAMPLE OF GLOBULAR CLUSTERS IN M87

                                MYUNG GYOON LEE

 Carnegie Observatories, 813 Santa Barbara Street, Pasadena, California 91101
                       Electronic mail: mglee@ociwl.edu

                                 DOUG GEISLER

      Cerro Tololo Inter-American Observatory, National Optical Astronomy
                 Observatories, Casilla 603, La Serena, Chile
                      Electronic mail: geisler@dao.nrc.ca

                                   ABSTRACT

    We present deep integrated Washington CCD photometry of the extremely
    populous globular cluster system of NGC 4486 (M87) in Virgo.  The
    metallicities of 407 of the best candidates with T1 < 22 have been
    estimated from the (C-T1) color.  These values are internally precise
    to ~0.15 dex and accurate to ~0.25 dex.  The mean metallicity of the
    globular clusters is [Fe/H] = -0.86 dex, with a formal standard error
    of the mean of 0.03 dex but a more realistic uncertainty of about 0.2
    dex.  This value is higher than that of the corresponding means of the
    globular clusters in the Galaxy and M31, but similar to those of the
    globular clusters in NGC 1399 and NGC 5128, as expected from the
    relative parent galaxy luminosities.  Approximately 10% of the clusters
    exceed solar abundance, similar to the case for the globular clusters
    in NGC 1399 and NGC 5128.  As found by Couture et al. [ApJS, 73, 671
    (1990)], there is a large metallicity dispersion at any radius, with a
    sigma ~ 0.65 dex.  However, in contrast to their result and that of
    previous small-field CCD studies, the globular clusters display a
    marked gradient in both mean (M-T1) and (C-T1) color with
    galactocentric distance.  The mean metallicity decreases by some 0.6
    dex over the radial extent of the cluster sample.  This result is
    consistent with the early photographic study by Strom et al. [ApJ, 245,
    416 (1981)].  The metallicity distribution function is remarkably
    similar to that of NGC 1399 found by Ostrov et al. [AJ, 105, 1762
    (1993)] using the same technique.  The two central cluster ellipticals
    show significant peaks at very similar metallicities, indicating
    similar formation and enrichment histories.  We also find that this
    structure in the metallicity distribution function persists to radii
    where the halo light is dominated by the cD envelope.