BVIPhotometry and the Luminosity Functions of the Globular Cluster M92

We present new BVI ground-based photometry and VI space-based photometry forthe globular cluster M92 (NGC 6341) and examine luminosity functions in B, V,and I containing over 50,000 stars ranging from the tip of the red giant branchto several magnitudes below the main sequence turn off. Once corrected forcompleteness, the observed luminosity functions agree very well withtheoretical models and do not show stellar excesses in any region of theluminosity function. Using reduced chi squared fitting, the new M92 luminosityfunction is shown to be an excellent match to the previously publishedluminosity function for M30. These points combine to establish that the"subgiant excess" found in previously published luminosity functions ofGalactic globular clusters are due to deficiencies in the stellar models usedat that time. Using up to date stellar models results in good agreement betweenobservations and theory. Several statistical methods are presented to best determine the age of M92.These methods prove to be insensitive to the exact choice of metallicity withinthe published range. Using [Fe/H]=-2.17 to match recent studies we find an ageof 14.2 plus or minus 1.2 Gyr for the cluster.Comment: 22 pages, 13 figures, 3 tables, accepted for publication in A