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

We carried out wide-field BVI CCD photometric observations of the GCs M3 andM13 using the BOAO 1.8 m telescope equipped with a 2K CCD. We present CMDs ofM3 and M13. We have found AGB bumps at V = 14.85 for M3 at V = 14.25 for M13.It is found that AGB stars in M3 are more concentrated near the bump, whilethose in M13 are scattered along the AGB sequence. We identified the RGB bumpof M3 at V = 15.50 and that of M13 at V = 14.80. We have estimated the ratios Rand R2 for M3 and M13 and found that of R for M3 is larger than that for M13while R2's for M3 and M13 are similar when only normal HB stars are used in Rand R2 for M13. However, we found that R's for M3 and M13 are similar while R2for M3 is larger than that for M13 when all the HB stars are included in R andR2 for M13. We have compared the observed RGB LFs of M3 and M13 with thetheoretical RGB LF of Bergbusch & VandenBerg at the same radial distances fromthe cluster centers as used in R and R2 for M3 and M13. We found "extra stars"belonging to M13 in the comparison of the observed RGB LF of M13 and thetheoretical RGB LF of Bergbusch & VandenBerg. In the original definition of Rof Buzzoni et al., N(HB) corresponds to the lifetime of HB stars in the RRLyrae instability strip at log T_eff = 3.85. So, the smaller R value resultingfor M13 compared with that for M3 in the case where only normal HB stars areincluded in R and R2 for M13 may be partially caused by "extra stars", and thesimilar R's for M3 and M13 in the case where the all HB stars are included in Rand R2 for M13 may be caused by "extra stars" in the upper RGB of M13. If"extra stars" in the upper RGB of M13 are caused by an effective "deep mixing"these facts support the contention that an effective "deep mixing" could leadto different HB morphologies between M3 and M13 and subsequent sequences.Comment: 24 pages, 7 figures, to be published in the A