Deep CCD photometry in globular clusters. III - M15

CCD photometry in U, V, and B wavelengths is presented for a field of 5 x 3 arcmin in the globular cluster M15. The photometric observations were carried out using the Cerro Tololo 4-m telescope in prime focus. The photometric data were used to obtain new estimates of reddening in M15 based on the bright field stars. New estimates of metallicity were also obtained by measuring the ultraviolet excess in the main sequence stars. The luminosity function of the cluster was studied down to V = 2.28 and was found to be consistent with a power-law mass function of n(M) = Q(M) sq rt alpha, where alpha is equal to about 2.5 + or - 1.0. Comparison with published data showed that the number of field stars in the red region of the cluster main sequence exceeded previous estimates by as much as 50 percent. The reddening of M15 was found to be E(B-V) = 0.11 + or - 0.04, and the ultraviolet excess relative to the Hyades cluster was delta(0.06) = 0.25 + or - 0.02. On the basis of the metal-poor isochrones obtained for the forbidden line emission of Fe/H and O/Fe, an age of 16 + or - 3 x 10 to the 9th years is estimated.