CCD PHOTOMETRY IN THE GLOBULAR-CLUSTER-M4

A V, B-V composite colour-magnitude diagram, based upon CCD photometry from V similar to 12 on the red giant branch to V similar to 25 on th e main sequence is presented for the globular cluster M4. The distance to M4, from fitting local subdwarfs to the lower main sequence, is (m - M)(V) = 12.84 +/- 0.19. The luminosity function of the cluster reac hes to M(V) > 11. At M(V) > 10 the luminosity function shows a turnove r. The mass function extends down to M similar to 0.19 M. and is quite flat, having a power-law index of x = -0.15 +/- 0.04 over the range s tudied. It is suggested that the most likely explanation for the obser ved flatness in the mass function is that the cluster has undergone ex tensive tidal stripping. The best match to theoretical isochrones is f or the case [Fe/H]= -1.27 and an age of 16 +/- 1 Gyr. A differential a ge comparison with NGC 362 shows that M4 is approximately 1.7 Gyr olde r. Finally, measurement of the small intrinsic colour spread on the su bgiant branches indicates that there is no strong evidence for any rea l spread in metallicity among cluster stars.