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Description
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.
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