PHOTOMETRIC CALIBRATION IN THE METAL-RICH GLOBULAR CLUSTER M69.

Photoelectric BV photometry is reported for sequence stars in the field of NGC 6637, a globular cluster of relatively high heavy-element abundance. The data are used to recalibrate the photographic color-magnitude (CM) diagram by Hartwick and Sandage (1968) for the cluster. Considerable systematic corrections to the previous photographic photometry are found to be needed in both V and (B - V), in the sense that the giant branch becomes both bluer and markedly steeper. The recalibrated photometric parameters describing the morphology of the CM diagram become V = 2.4, (B - v) . = 0.95, and S = 5, and the distance modulus is estimated as (m - M)v = 15.6. Key words: photometry-globular cluster