Globular Clusters and Horizontal Branch

Abstract

An analysis of available Galactic globular cluster data on metallicity, ages, the distribution of stars on the horizontal branch and the distribution of the periods of RR0 Lyr variables showed that: 1. The latter two characteristics can be used for determining the Oosterhoff type. 2. The metallicities of the observed OoI and OoII clusters overlap in a narrow interval -1.65$<$[Fe/H]$<$1.52. 3. The OoII clusters are characterized by R-B$<$0, a statistically significant relation (r=0.97) between the relative number of B(BS) and V(VS) stars on the horizontal branch. 4. The OoI clusters divide into two groups: R-B$<$0 and R-B$>$0 with a relation between B and R (r=0.90). The former clusters do not show a relation between VS and RS stars and the latter a relation between VS and BS stars on the horizontal branch. 5. The oldest clusters are characterized by BS close to 1 and the youngest by R close to 1.