BV photometry of the RR Lyrae variables of the globular cluster M3

We present new BV CCD photometry, light curves, and ephemerides for 207 RR Lyrae variables in the globular cluster M3. For 127 of these we present observed minus calculated (O-C) diagrams. The data were acquired on observing runs in 1992 May, 1993 April, and 1997 June. In all 189 BV pairs were obtained. Estimates of fundamental photometric parameters are presented, including intensity- and magnitude-averaged B and V magnitudes and magnitude-averaged colors, pulsation periods, and pulsation amplitudes. In many cases we find periods substantially different from those previously reported. For 30 variables, periods are reported here for the first time. A color-magnitude diagram is given in which the regions occupied by RRab and RRc variables show little or no overlap with each other or with the nonvariable horizontal branch. The boundaries of the instability strip for M3 are determined. Period changes are determined and the implications for horizontal-branch evolution are discussed. Roughly a dozen variables were found to be fainter than the zero-age horizontal branch, suggesting smaller-than-average core masses. This may be related to the location of the stars in the cluster's central region.