The structure and stellar content of globular clusters. II - Star counts and main-sequence luminosity functions for 47 Tuc, NGC 6397, and NGC 6752

Main-sequence luminosity functions and radial distributions of stars are determined over a range in mass that substantially exceeds that of previous work. Extensive star count data are presented for three nearby globular clusters: 47 Tuc, NGC 6397, and NGC 6752. The counting technique, background determinations, and crowding corrections and errors are discussed in detail, as well as the limiting magnitude determinations. Clear evidence is found for mass segregation in Tuc 47, but in the outer parts of all clusters, the density distributions are consistent with a limiting cluster radius that is independent of stellar mass as required by a tidal cutoff. The main-sequence luminosity functions for the clusters are found to be different, and while this is partly due to mass segregation effects, there are probably real differences between the current mass functions.