THE DISTANT GLOBULAR-CLUSTER NGC 6229 AND ITS RELATION TO OTHER OUTER HALO CLUSTERS

We present CCD-based BV photometry for over 1100 stars in and around the globular cluster NGC 6229. For the first time, the cluster's entire giant branch and its horizontal branch are delineated, from which metallicity ([Fe/H] approximately - 1.4) and distance (d(o) approximately 28 kpc; d(GC) approximately 27 kpc) estimates ensue. NGC 6229 is found to have a relatively blue horizontal branch for its intermediate metallicity, which is unusual for an outer halo cluster. Its low R value (defined as N(HB)/N(RG)) hints that the blue color of its horizontal branch is due to a lower than average helium abundance. Three possible new variable stars are identified, including one RR Lyrae and two long-period variables. We present a brief review of our knowledge of basic data for the 13 globular clusters lying more than 24 kpc from the Galactic center. The unusually red horizontal branch phenomenon is common only among the outermost clusters. An average R value for these clusters suggests the effect is not caused by an overabundance of helium. The Oosterhoff dichotomy apparently persists into the outer halo, although the number of clusters with RR Lyrae variables is small.