BV photometry of RR Lyrae variables in the globular cluster M92

Abstract

We present BV CCD photometry for 7 RR Lyrae variables in the globular cluster M92 (NGC 6341). New ephemerides are computed, and V, B, and B-V light curves are given. A color-magnitude diagram based on 2 V and 2 B short exposures is given, reaching from above the horizontal branch to below the main sequence turn-off. A comparison with results from other workers shows we agree with the photometry of Cathey (1974) and Stetson and Harris (1988). We study also the timing of the secondary bumps in the light curves of 5 of the RRab variables, finding it to be consistent with prediction from the echo model. Expansion radii derived from radial velocities are not consistent with the photospheric infall model of the secondary bump.