BVRI CCD Photometry of the Globular Cluster M55 (NGC 6809)

The paper presents BVRI photometry of two neighboring fields in the globular cluster M55 (NGC 6809) observed with a CCD camera and the 2.2-m telescope at ESO/La Silla. A comparison of BV color-magnitude diagram (CMD) of the M55 with those of Lee (1977) and Schade et al. (1988) showed generally good agreement down to about a magnitude below the main-sequence turnoff, although deviations at the extreme values of color and magnitude were found. The four-color CMDs fitted to the theoretical isochrons of VandenBerg and Bell (1985) give a best age of 14.5 +/-3 Gyr.