Two-color CCD Photometry of Variable Stars in NGC 7006

Abstract

B and V CCD photometry from 1984 through 1994 is presented for 50 RR Lyrae stars and two red variable stars in the globular cluster NGC 7006. New determinations of pulsation periods and period change rates are given and used to plot B light curves. The new photometry is combined with previously published photometry obtained from photographic plates taken in the 1930s, the 1950s and 1984 and used to derive O - C diagrams and new period change rates. V light curves based on the CCD data are also displayed, and colors derived from mean values of B and V are given. Period-amplitude diagrams and the color-magnitude diagram for the variables are shown. The dereddened blue and red edges to the instability strip in the cluster are found to be at (B-V)0 = 0.14 and 0.38. The period change rates have been revised from those given in an earlier paper and the new median period change rate is found to be +0.03, close to that predicted by the Yale evolutionary models.