Rebounding Cores to Build Star Cluster Multiple Populations
  We present a novel approach to the riddle of star cluster multiple
populations. Stars form from molecular cores. But not all cores form stars.
Following their initial compression, such 'failed' cores re-expand, rather than
collapsing. We propose that their formation and subsequent dispersal regulate
the gas density of cluster-forming clumps and, therefore, their core and star
formation rates. Clumps for which failed cores are the dominant core type
experience star formation histories with peaks and troughs. In contrast, too
few failed cores results in smoothly decreasing star formation rates. We
identify three main parameters shaping the star formation history of a clump:
the star and core formation efficiencies per free-fall time, and the time-scale
on which failed cores return to the clump gas. The clump mass acts as a scaling
factor. We use our model to constrain the density and mass of the Orion Nebula
Cluster progenitor clump, and to caution that the star formation histories of
starburst clusters may contain close-by peaks concealed by stellar age
uncertainties. Our model generates a great variety of star formation histories.
Intriguingly, the chromosome maps and O-Na anti-correlations of old globular
clusters also present diverse morphologies. This prompts us to discuss our
model in the context of globular cluster multiple stellar populations. More
massive globular clusters exhibit stronger multiple stellar population
patterns, which our model can explain if the formation of the polluting stars
requires a given stellar mass threshold.
