The First Population II Stars Formed in Externally Enriched Mini-halos
  We present a simulation of the formation of the earliest Population II stars,
starting from cosmological initial conditions and ending when metals created in
the first supernovae are incorporated into a collapsing gas-cloud. This occurs
after a supernova blast-wave collides with a nearby mini-halo, inducing further
turbulence that efficiently mixes metals into the dense gas in the center of
the halo. The gas that first collapses has been enriched to a metallicity of Z
~ 2e-5 Zsun. Due to the extremely low metallicity, collapse proceeds similarly
to metal-free gas until dust cooling becomes efficient at high densities,
causing the cloud to fragment into a large number of low mass objects. This
external enrichment mechanism provides a plausible origin for the most
metal-poor stars observed, such as SMSS J031300.36-670839.3, that appear to
have formed out of gas enriched by a single supernova. This mechanism operates
on shorter timescales than the time for low-mass mini-halos (M < 5e5 Msun) to
recover their gas after experiencing a supernova. As such, metal-enriched stars
will likely form first via this channel if the conditions are right for it to
occur. We identify a number of other externally enriched halos that may form
stars in this manner. These halos have metallicities as high as 0.01 Zsun,
suggesting that some members of the first generation of metal-enriched stars
may be hiding in plain sight in current stellar surveys.
