THE STELLAR POPULATION OF THE GLOBULAR-CLUSTER M-3 .2. CCD PHOTOMETRYOF ADDITIONAL 10,000 STARS

We present BVI CCD photometry for more than 10,000 stars in the innerm ost region (0.3' < r <similar to 4') of the globular cluster M 3. When added to the previous photographic photometry by Buonanno et al. (199 4) reaching as far as r similar to 7', this results in an homogeneous data-set including about 19,000 stars measured in this cluster, which can be now regarded as one of the main templates for stellar populatio n studies. Our main results, from the new colour-magnitude diagrams (C MD), are: 1. Completeness has been achieved for all objects at V less than or equal to 18.6 and 0.3' < r < 7'. 2. Our new independent photom etric calibration is redder than the old calibration (Sandage and Kate m 1982) in the blue range, and bluer in the reddest part of the CMD. T his colour term has important consequences on some issues (e.g. metall icity, period-shift effect, etc.). 3. The metallicity derived from the photometric indicators (B - V)(0,g) and Delta 1.4 is [Fe/H]similar to -1.45, i.e. significantly higher than the value -1.66 generally used s o far. This is in very good agreement with the most recent high resolu tion spectroscopic studies of individual stars. 4. There is indication of the presence of a very faint and blue extension of the HB, althoug h scarcely populated. 5. The population ratios of HB, RGB and AGB star s confirm the value previously found for the helium content, i.e. Y=0. 23+/-0.02. 6. There is a significant population of blue straggler star s, although the exact number must await HST data for a better resoluti on in the very central regions.