For the well observed 16 globular clusters with known metal abundance (Z), the helium abundances (Y) and ages are determined by various methods, and the relations between Y, Z and age are examined. The luminosity L R R of RR Lyrae stars is known to be dependent of evolutionary models and pulsation theory in the sense that the pulsation theory and horizontal branch (HB) models yield the anticorrelation between L R R and Z whereas main sequence (MS) and red giant branch (RGB) models yield the direct correlation between them. Similarly the anticorrelation between Y and Z is obtained from the HB models and pulsation theory whereas the direct correlation between them is obtained when the RGB model is applied. The current evolutionary models yield the anticorrelation between Z and age of clusters whenever the direct correlation between Y and Z holds. However when the anticorrelation between Y and Z is applied for age determination, the similar age of clusters is obtained as shown by Sandage (1982b). The ages, which are determined by the fitting of C-M diagrams to isochrones in the ( M v , B-V)-plane, suggest the two different chemical enrichment processes, which could be accounted for by the disk-halo model for the chemical evolution of the Galaxy (Lee and Ann 1981). Also it is known that the R-method is very useful for Y-determination and the derived Y's show the increasing rate of Δ Y Δ Z ≃ 0.5 which is comparable to the observed value of Δ Y Δ Z ≃ 0.3 from HII regions and planetary nebulae by Peimbert and Torres-Peimbert (1976). In this case, the age-metallicity relation of globular clusters could be explained by the disk-halo model.

ABSTRACT
Ⅰ. INTRODUCTION
Ⅱ. DISTANCE OF GLOBULAR CULSTERS
Ⅲ. HELIUM ABUNDANCE
Ⅳ. AGE AND ITS RELATION WITH ABUNDANCE
Ⅴ. CONCLUSION AND DISCUSSION
REFERENCES

• LEE SEE-WOO(Department of Astronomy, Seoul National University)