Detection of multiple stellar populations in extragalactic massive
  clusters with JWST
  The discovery both through spectroscopy and photometry of multiple stellar
populations in Galactic globular clusters, and in Magellanic Clouds' massive
intermediate-age and old clusters, has led to a major change in our views about
the formation of these objects. To date, none of the proposed scenarios is able
to explain quantitatively all chemical patterns observed in individual
clusters, and an extension of the study of multiple populations to resolved
extragalactic massive clusters beyond the Magellanic Clouds would be welcome,
for it would enable to investigate and characterize the presence of multiple
populations in different environments and age ranges. To this purpose, the
James Webb Space Telescope can potentially play a major role. On the one hand,
the JWST promises direct observations of proto-globular cluster candidates at
high redshift; on the other hand, it can potentially push to larger distances
the sample of resolved clusters with detected multiple populations. In this
paper we have addressed this second goal. Using theoretical stellar spectra and
stellar evolution models, we have investigated the effect of multiple
population chemical patterns on synthetic magnitudes in the JWST infrared
NIRCam filters. We have identified the colours (F150W-F460M), (F115W-F460M) and
pseudocolours C_{F150W,F460M,F115W}=(F150W-F460M)-(F460M-F115W),
C_{F150W,F277W,F115W}=(F150W-F277W)-(F277W-F115W), as diagnostics able to
reveal the presence of multiple populations along the red giant branches of old
and intermediate age clusters. Using the available on-line simulator for the
NIRCam detector, we have estimated that multiple populations can be potentially
detected --depending on the exposure times, exact filter combination used, plus
the extent of the abundance variations and the cluster [Fe/H]--out to a
distance of about 5Mpc (approximately the distance to the M83 group).
