On the metallicity distribution of the peculiar globular cluster M22
  In our previous study, we showed that the peculiar globular cluster (GC) M22
contains two distinct stellar populations, namely the Ca-w and Ca-s groups with
different physical properties, having different chemical compositions, spatial
distributions and kinematics. We proposed that M22 is most likely formed via a
merger of two GCs with heterogeneous metallicities in a dwarf galaxy
environment and accreted later to our Galaxy. In their recent study,
Mucciarelli et al. claimed that M22 is a normal mono-metallic globular cluster
without any perceptible metallicity spread among the two groups of stars, which
challenges our results and those of others. We devise new strategies for the
local thermodynamic equilibrium (LTE) abundance analysis of red giant branch
(RGB) stars in GCs and show there exists a spread in the iron abundance
distribution in M22.
