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 colours 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 abundance within the cluster. Use is made of an extensive optical/near-infrared observational data set acquired with a large-array CCD detector and the Johnson V and I filters. The results of this photometry, which is accurate to within a few millimagnitudes for the brighter stars, are used to compile a colour–magnitude diagram.
The analysis finds that in a metal-rich M5 ([Fe/H]=−1.2) the extent of any metal inhomogeneity, Δ[Fe/H], is less than ±0.1 dex, and in a metal-poor M5 ([Fe/H]=−1.5) then     . (The literature contains a range of derived values of metallicity for M5.)