Different Characteristics of the Bright Branches of the Globular Clusters M15 and M92

We carried out relatively wide-field BVI CCD photometric observations of the globular clusters M15 (NGC 7078) and M92 (NGC 6341) using the 1.8 m telescope of the Bohyun Optical Astronomy Observatory. We present color-magnitude diagrams ( V vs. B - V , V vs. V - I , and V vs. B - I ) of M15 and M92. We found asymptotic giant branch (AGB) bumps at V = 15.20 ± 0.05 mag and V = 14.50 ± 0.05 mag for M15 and M92, respectively. We identified the red giant branch (RGB) bumps of the two clusters. We have estimated the population ratios R and R 2 for M15 and M92 in two cases: when only normal horizontal-branch (HB) stars are used and when all the HB stars are used. We have compared the observed RGB luminosity functions of M15 and M92 with the theoretical RGB luminosity functions of Bergbusch & VandenBerg and found no significant "extra stars" in the comparisons. This implies that the HB morphology difference between M15 and M92 is not certain due to the results of deep mixing in the RGB sequence.