CCD PHOTOMETRY OF VARIABLE STARS IN THE GLOBULAR CLUSTER RU 106

Abstract

BV photometry is presented for 12 RR Lyr variables discovered in the presumably young galactic globular cluster Ruprecht 106. All variables are type RRab, and their periods span a narrow range from 0.574 to 0.652 day. We report also on the discovery of 3 SX Phe variables among the cluster blue stragglers. A likely background RR Lyr variable and two foreground contact binaries were also found in the cluster field. The reddening of Ruprecht 106 is estimated at E(B-V)=0.20 based on the (B-V) colors exhibited by the cluster RR Lyr variables at minimum light. Analysis of the "period" versus "amplitude" and "period" versus "rise-time" diagrams suggests similar metallicities of Ruprecht 106 and M3. A peak (or bump) is present in the luminosity function of the red giant branch of Ruprecht 106. Its position relative to the horizontal branch is consistent with a cluster metallicity of [Fe/H]>= -1.6.