DEEP CCD PHOTOMETRY AND VARIABLE-STARS IN THE METAL-RICH GLOBULAR-CLUSTER M71

Two sets of observations of the metal-rich globular cluster M71 are presented. The first uses deep CCD exposures to derive a fiducial in V, B - V and compares this with a cluster of similar metallicity, 47 Tuc. Comparison with oxygen enhanced theoretical isochrones leads to age estimates for M71 of from is similar to 14 +/- 2 Gyr to is similar to 16 +/- 2 Gyr. Within the limits imposed by the quality of the data, no significant age difference between the two clusters is found. The second set of 73 frames is used to search an overlapping 67" X 104" area of the cluster for variable stars. Light curves and phase diagrams (where appropriate) are presented for all four of the variables discovered. One variable blue straggler (or SX Phe star) has been identified with a period of 0.050d. Values for its mass depend, of course, on the assumed pulsation mode-(0.90 +/- 0.47) M. for the first overtone mode, and (1.57 +/- 0.83) M. for the fundamental mode. One of the variables, with a 0.0582d period, but with a magnitude 1.75m below the main sequence turnoff may be a field star. Two candidate eclipsing binary systems were also found. The most likely orbital period of one is 0.372d. This value, and the shape of the light curve, suggest that it could be a W UMa. type variable. No period was obtainable for the other candidate binary due to a lack of phase coverage. Further data is needed to confirm and strengthen these claims, and to check for cluster membership.