Deep CCD photometry of stars in the globular cluster M3

We present CCD photometry of faint stars in the globular cluster M3. The observations reach down to V≅23 mag., with a sample of approximately 5000 stars. The resulting colour magnitude diagram (CMD) has a turn-off significantly redder than those obtained in previous studies. Age and distance are derived by fitting the observed mean line to the theoretical isochrones by Chieffi and Straniero. The dependence on the assumed metallicity and colour excess values is studied in some detail. In general, theoretical and observed loci are in excellent agreement yielding 14.85 < (m-M)v < 14.93 mag and 16 < t < 19 Gyr, depending on the different assumptions about reddening and metallicity. Finally, the luminosity function (LF) is presented. When incompletenesses is taken into account, the observed LF appears in good agreement with the curve predicted by theoretical models computed assuming a mass function with α = 2.5