THE ASTRONOMICAL JOURNAL    VOLUME 112, NUMBER 3, PAGE 1061      SEPTEMBER 1996

     LUMINOSITY FUNCTIONS FOR POST-TURNOFF STARS IN GLOBULAR CLUSTERS. II.
                                   NGC 7099

                              PETER A. BERGBUSCH

                 Department of Physics, University of Regina,
                     Regina, Saskatchewan S4S 0A2, Canada
                Electronic mail: bergbush@deneb.phys.uregina.ca


                                   ABSTRACT

    New BV CCD photometry for the bright stars in cluster fields centered
    on the core of NGC 7099 is presented.  The morphology of the LF though
    the turnoff region is similar to that found in other metal-poor
    clusters in that the relative number of turnoff to giant stars is lower
    than predicted by canonical models.  Comparisons with evolutionary
    sequences of horizontal branch stars suggest a reddening E(B-V) = 0.06
    and a distance modulus (m-M)_V = 14.83.  Isochrone fits to [Fe/H] =
    -2.03, [O/Fe] = +0.70 models are consistent with an age of at least 14
    Gyr.  The model LF for this age accurately predicts the brightness of
    the tip of the red giant branch (RGB) as well as the location of the
    break which signals the transition from the base of the RGB to the main
    sequence.  There is an indication that the evolutionary pause on the
    RGB, which manifests itself as a bump in the LF, occurs one magnitude
    fainter than the models predict.  The excess of HB stars with respect
    to giants is confirmed and implies a helium abundance Y = 0.28, which
    is higher than that found in other metal-poor globular clusters from
    the R method.  From a comparison with the metal-rich, blue horizontal
    branch cluster NGC 288, it is argued that age cannot by itself be the
    solution to the second parameter problem.