Signatures of multiple stellar populations in unresolved extragalactic
  globular/ young massive star clusters
  We present an investigation of potential signatures of the formation of
multiple stellar populations in recently formed extragalactic star clusters.
All of the Galactic globular clusters for which good samples of individual
stellar abundances are available show evidence for multiple populations. This
appears to require that multiple episodes of star formation and light element
enrichment are the norm in the history of a globular cluster. We show that
there are detectable observational signatures of multiple formation events in
the unresolved spectra of massive, young extragalactic star clusters. We
present the results of a pilot program to search for one of the cleanest
signatures that we identify - the combined presence of emission lines from a
very recently formed population and absorption lines from a somewhat older
population. A possible example of such a system is identified in the Antennae
galaxies. This source's spectrum shows evidence of two stellar populations with
ages of 8 Myr and 80 Myr. Further investigation shows that these populations
are in fact physically separated, but only by a projected distance of 59 pc. We
show that the clusters are consistent with being bound and discuss the
possibility that their coalescence could result in a single globular cluster
hosting multiple stellar populations. While not the prototypical system
proposed by most theories of the formation of multiple populations in clusters,
the detection of this system in a small sample is both encouraging and
interesting. Our investigation suggests that expanded surveys of massive young
star clusters should detect more clusters with such signatures.
