2000/10/17 by J. Kałużny, J. Kaluzny, A. Olech +1 · 3 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/319411
published as 2001, AJ, 121, 1533 · submitted to AJ, 31 pages, 14 figures; additional data and full resolution finding charts available at ftp://cfa-ftp.harvard.edu/pub/kstanek/NGC6934
arxiv created 2000/10/17 · openalex publication_date 2001/03/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We present CCD BVI 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, five RRc stars, two eclipsing binaries of W UMa-type, one SX Phe star, and three 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 log L / L ⊙ = 1.72, effective temperature T eff = 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 M V = 0.81, [Fe/H] = -1.53 and T eff = 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 HST -based V -band photometry of NGC 6934 recently presented by Piotto et al. Among analyzed sample of RR Lyr stars we have detected a short period and low amplitude variable which possibly belongs to the group of second overtone pulsators (RRe subtype variables). The BVI photometry of all variables is available electronically via anonymous ftp. The complete set of the CCD frames is available upon request.