The metal homogeneity of the globular star cluster M5

This work is concerned with the precision measurement of the magnitudes of the stars across a large field of the galactic globular cluster M5. The col ours of the red giants are subjected to a thorough statistical analysis in order to quantify the extent of any star-to-star variations in metal abunda nce within the cluster. Use is made of an extensive optical/near-infrared o bservational data set acquired with a large-array CCD detector and the John son V and I filters. The results of this photometry, which is accurate to w ithin a few millimagnitudes for the brighter stars, are used to compile a c olour-magnitude diagram. The analysis finds that in a metal-rich M5 ([Fe/H] = -1.2) the extent of an y metal inhomogeneity, Delta[Fe/H], is less than +/-0.1 dex, and in a metal -poor M5 ([Fe/H] = -1.5) then Delta[Fe/H]less than or equal to(-0.15)(+0.12 ) dex. (The literature contains a range of derived values of metallicity fo r M5.).