Intermediate resolution spectra at the Ca II triplet have been obtained for 55 candidate red giants in the field of the globular cluster M22 with the VLT/FORS2 instrument .
Spectra were also obtained for a number of red giants in standard globular clusters to provide a calibration of the observed line strengths with overall abundance [ Fe/H ] .
For the 41 M22 member stars that lie within the V - V _ { HB } bounds of the calibration , we find an abundance distribution that is substantially broader than that expected from the observed errors alone .
We argue that this broad distribution can not be the result of differential reddening .
Instead we conclude that , as has long been suspected , M22 is similar to \omega Cen in having an intrinsic dispersion in heavy element abundance .
The observed M22 abundance distribution rises sharply to a peak at [ Fe/H ] \approx –1.9 with a broad tail to higher abundances : the highest abundance star in our sample has [ Fe/H ] \approx –1.45 dex .
If the unusual properties of \omega Cen have their origin in a scenario in which the cluster is the remnant nucleus of a disrupted dwarf galaxy , then such a scenario likely also applies to M22 .