THE VARIABLE STAR POPULATION IN THE GLOBULAR CLUSTER NGC 6934

Abstract

We report an analysis of new V and I CCD time-series photometry of the globular cluster NGC 6934. Through the Fourier decomposition of the RR Lyrae light curves the mean values of [Fe/H] and the distance of the cluster were estimated; we found: [Fe/H]UV ES = −1.48 ± 0.14 and d = 16.03 ± 0.42 kpc, and [Fe/H]UV ES = − 1 .43 ± 0 .11 and d = 15 .91 ± 0 .39 kpc, from the calibrations of RRab and RRc stars respectively. Independent distance estimations from SX Phe and SR stars are also discussed. Individual absolute magnitudes, radii and masses are also reported for RR Lyrae stars. We found 12 new variables: 4 RRab, 3 SX Phe, 2 W Virginis (CW) and 3 semi-regular (SR). The inter-mode or “either-or” region in the instability strip is shared by the RRab and RRc stars. This characteristic, observed only in some OoI clusters and never seen in an OoII, is discussed in terms of mass distribution in the ZAHB.