ATMOSPHERIC PARAMETERS AND METALLICITIES FOR 2191 STARS IN THE GLOBULAR CLUSTER M4

We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. For 322 red giant branch (RGB) stars with V [< or =] 14.7, we obtain a nearly constant metallicity, [left angle bracket][Fe/H][right angle bracket]) = -1.07 ([sigma] = 0.02). No difference in the metallicity at the level of 0.01 dex is observed between the two RGB sequences identified by Monelli et al. For 1869 subgiant and main-sequence stars with V > 14.7, we obtain [left angle bracket][Fe/H][right angle bracket] = -1.16 ([sigma] = 0.09) after fixing the microturbulent velocity.