1995A&A...301..675B

The core of the Galactic globular cluster Messier 3 (NGC 5272) has been imaged through the f/96-F140W, f/96-F220W and f/96-F346M ultraviolet filters of the Faint Object Camera onboard the Hubble Space Telescope (HST) down to an ultraviolet magnitude of ∼20. We measure a high specific frequency of blue stragglers stars (BSS), f_BSS=0.29 in the observed region. This is about three times the maximum value previously computed from UVI HST Wide Field and Planetary Camera -I observations of the core of M3. Part of this discrepency may be explained by the small size and the location of the surveyed area but the major part of the difference is the lower efficiency of the UVI-based detection. Accounting for the high density in the central area surveyed, primordial binaries are not likely to have survived the globular cluster lifetime. This new value suggests that the dynamical action of the globular cluster can significantly increase the production of BSS through stellar collisions in the core of M3. The ratio of the number of blue horizontal branch (BHB) to red horizontal branch (RHB) stars n_BHB/(n_BHB+n_RHB) is found to be ∼0.50, very similar to the external value. The number of BHB (2-3) and RHB (3-4) stars are consistent with that expected from the overall radial distribution of these objects with only one possible RHB in excess. This object in excess may possibly be interpreted as a BSS progeny located on the horizontal branch.