THE ASTRONOMICAL JOURNAL    VOLUME 109, NUMBER 3, PAGE 1131          MARCH 1995

         INFRARED ARRAY PHOTOMETRY OF METAL-RICH GLOBULAR CLUSTERS.
                        I. TECHNIQUES AND FIRST RESULTS

            LESLIE E. KUCHINSKI, JAY A. FROGEL, AND D. M. TERNDRUP

   Department of Astronomy, The Ohio State University, 174 West 18th Avenue,
                              Columbus Ohio 43210
        Electronic mail: {lek,frogel,terndrup}@payne.mps.ohio-state.edu

                                 S. E. PERSSON

         The Observatories of the Carnegie Institution of Washington,
             813 Santa Barbara Street, Pasadena, California 91101
                    Electronic mail: persson@lynx.ociw.edu


                                   ABSTRACT

    As a first step in investigating the properties of heavily reddened,
    metal-rich globular clusters, we present JHK colors and magnitudes for
    four objects: NGC 5927, NGC 6712, NGC 6838 (M71), and Terzan 2.  These
    data begin near the top of the giant branch (GB) and extend to stars
    six magnitudes fainter, reaching below the horizontal branch (HB).  We
    use our sample and previously published data for two other clusters, 47
    Tucanae and M69, to develop techniques for deriving basic properties
    such as metallicity and distance modulus from observable parameters of
    cluster color-magnitude diagrams (CMDs) in the near-IR.  We also
    analyze the horizontal branches of the clusters in an attempt to set
    constraints on mass loss for first-ascent giants.  We find that the
    slope of the linear fit to the GB stars brighter than the HB can be
    used to predict metallicity to an accuracy of +/- 0.25 dex for clusters
    with [Fe/H] between -1.0 and -0.3.  There appears to be no significant
    dependence on [Fe/H] for other reddening-free indices measured from the
    CMD, including the width of the HB and the separation between the GB
    and HB at the level of the HB.  Using the clusters in our sample that
    have known distances, we derive a value of <M_K0(HB)> = -1.15 +/- 0.10
    for the extinction-corrected absolute K magnitude of the HB.  This
    provides a means of determining the distance to clusters for which only
    infrared CMDs are available.  We derive a distance modulus to Terzan 2
    of 14.37 +/- 0.2 which places it within a few hundred parsecs of the
    galactic center.  In the J-H,H-K diagram, Terzan 2 giants are located
    near the Baade's Window giants rather than in the region populated by
    nearly all other globular cluster stars.  The GB of stars in the field
    around Terzan 2 has a slope that implies [Fe/H] = +0.1, comparable to
    that in Baade's Window.