New insights on the origin of multiple stellar populations in globular
  clusters
  In order to investigate the origin of multiple stellar populations in the
halo and bulge of the Milky Way, we have constructed chemical evolution models
for the low-mass proto-Galactic subsystems such as globular clusters (GCs).
Unlike previous studies, we assume that supernova blast waves undergo blowout
without expelling the pre-enriched gas, while relatively slow winds of massive
stars (WMS), together with the winds and ejecta from low and intermediate mass
asymptotic-giant-branch stars (AGBs), are all locally retained in these less
massive systems. We find that the observed Na-O anti-correlation in metal-poor
GCs can be reproduced, when multiple episodes of starbursts are allowed to
continue in these subsystems. Specific star formation history (SFH) with
decreasing time intervals between the stellar generations, however, is required
to obtain this result, which is in good agreement with the parameters obtained
from our stellar evolution models for the horizontal-branch. The "mass budget
problem" is also much alleviated by our models without ad-hoc assumptions on
star formation efficiency (SFE) and initial mass function (IMF). We also
applied these models to investigate the origin of super-helium-rich red clump
stars in the metal-rich bulge as recently suggested by Lee et al. (2015). We
find that chemical enrichments by the WMS can naturally reproduce the required
helium enhancement (dY/dZ = 6) for the second generation stars. Disruption of
proto-GCs in a hierarchical merging paradigm would have provided helium
enhanced stars to the bulge field.
