Abstract
We present the results of time-series CCD photometry of the globular cluster NGC 6981 for which no previous CCD photometry exist. Accurate photometry was achieved by the technique of difference image analysis. This allows to correctly classify the known variable stars, corroborate their variability and to discover new variables. In this paper we report 11 new RR Lyrae stars, 3 SX Phe. We show that 20 stars previously classified as variables are in fact non-variable and confirm the variability of 29 stars. News ephemerides are provided for all the variables in the cluster. By using the Fourier decomposition of light curves and semi-empirical calibrations available in the literature for RR Lyrae stars, we determined the physical parameters of these stars and hence the mean metallicity and distance of the cluster as [Fe/H]=-1.48±0.03 in the Zinn & West (1984) scale; and ≈ 16.73±0.36 kpc.
