THE ASTRONOMICAL JOURNAL    VOLUME 109, NUMBER 2, PAGE 639        FEBRUARY 1995

         HST OBSERVATIONS OF THE CORE OF THE GLOBULAR CLUSTER NGC 6624

                         CRAIG SOSIN AND IVAN R. KING

 Department of Astronomy, University of California, Berkeley, California 94720
      Electronic mail: csosin@aster.berkeley.edu, king@glob.berkeley.edu


                                   ABSTRACT
    
    We have used the Faint Object Camera on the Hubble Space Telescope
    (HST) to observe three fields near the center of the post-collapse
    globular cluster NGC 6624 in B and V.  We use individual stellar
    positions and a maximum-likelihood technique to measure a position for
    the cluster center.  We then transfer this position and the position of
    the x-ray source 4U 1820-30 to right ascension and declination, and
    correct an error of 1.8" in an earlier paper.  From star counts, we
    obtain a density profile, with a power-law cusp of slope -0.84 +/-
    0.16.  No flat core is evident.  We construct color-magnitude diagrams
    down to the main-sequence turnoff near the cluster center, and more
    than three magnitudes below the turnoff in the outermost field at
    r=28".  The former diagram reveals a central population of blue
    stragglers, which has not previously been observed in this cluster.
    These blue stragglers are quite similar in specific frequency to those
    recently observed by HST in the core of 47 Tuc, and their presence adds
    to the growing evidence of stellar interactions in dense
    globular-cluster cores.