The BV-photographic photometry was made for 1714 stars (V<19.5) in NGC 6752. The C-M diagram of this cluster shows an unusually extended blue horizontal branch ( V = 13.5 ∼ 17.8 ) with a wide gap ( V = 16 ∼ 16.7 ) and the well defined giant branch with gaps at V=13.85 and 16.2. The turnoff point is defined at V = 17.25 ± 0.15 and (B-V) = 0.46 ± 0.02 . If we take V H B = 13.85 for NGC 6752, then Δ V = 2.80 , ( B − V ) 0 , g = 0.76 a n d Δ V T O = 3.40 and the chemical abundance is estimated to be [Fe/H]=-1.67 or Z = 4.3 × 10 − 4 a n d Y = 0.26 . Some other physical parameters of this cluster are derived and compared with those for the well observed clusters M 3, M 13, M 15 and M 92.

ABSTRACT
Ⅰ. INTRODUCTION
Ⅱ. OBSERVATIONS
Ⅲ. THE C-M DIAGRAM
Ⅳ. GAPS ON GIANT AND BLUE HORIZONTAL BRANCHES
Ⅴ. HORIZONTAL BRANCH AND METAL ABUNDANCE
Ⅵ. PHYSICAL PARAMETERS
ACKNOWLEDGEMENT
REFERENCES

• SEE-WOO LEE(Department of Astronomy, Seoul National University)
• R. D. CANNON(U.K. 48-inch Schmidt Telescope Unit, Edinburgh, Scotland)