0 Image - Subtraction Photometry of Variable Stars in the Field of the Globular Cluster NGC 6934

We present CCD BV I photometry of 85 variable stars from the field of the globular cluster NGC 6934. The photometry was obtained with the image subtraction package ISIS. 35 variables are new identifications: 24 RRab stars, 5 RRc stars, 2 eclipsing binaries of W UMa-type, one SX Phe star, and 3 variables of other types. Both detected contact binaries are foreground stars. The SX Phe variable belongs most likely to the group of cluster blue stragglers. Large number of newly found RR Lyr variables in this cluster, as well as in other clusters recently observed by us, indicates that total RR Lyr population identified up to date in nearby galactic globular clusters is significantly (> 30%) incomplete. Fourier decomposition of the light curves of RR Lyr variables was used to estimate the basic properties of these stars. From the analysis of RRc variables we obtain a mean mass of M = 0.63 M⊙, luminosity logL/L⊙ = 1.72, effective temperature Teff = 7300 and helium abundance Y = 0.27. The mean values of the absolute magnitude, metallicity (on Zinn’s scale) and effective temperature for RRab variables are: MV = 0.81, [Fe/H] = −1.53 and Teff = 6450, respectively. From the B − V color at minimum light of the RRab variables we obtained the color excess to NGC 6934 equal to E(B − V ) = 0.09 ± 0.01. Different calibrations of absolute magnitudes of RRab and RRc available in literature were used to estimate apparent distance modulus of the cluster: (m − M)V = 16.09 ± 0.06. We note a likely error in the zero point of the Based on observations obtained with the 1.2 m Telescope at the F. L. Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland ([email protected]) Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland ([email protected]) Hubble Fellow Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS20, Cambridge, MA 02138, USA ([email protected])