The stochastic enrichment of Population II stars
  We investigate the intrinsic scatter in the chemical abundances of a sample
of metal-poor ([Fe/H]<-2.5) Milky Way halo stars. We draw our sample from four
historic surveys and focus our attention on the stellar Mg, Ca, Ni, and Fe
abundances. Using these elements, we investigate the chemical enrichment of
these metal-poor stars using a model of stochastic chemical enrichment.
Assuming that these stars have been enriched by the first generation of massive
metal-free stars, we consider the mass distribution of the enriching population
alongside the stellar mixing and explosion energy of their supernovae. For our
choice of stellar yields, our model suggests that the most metal-poor stars
were enriched, on average, by N*=5^{+13}_{-3} (1 sigma) Population III stars.
This is comparable to the number of enriching stars inferred for the most
metal-poor DLAs. Our analysis therefore suggests that some of the lowest mass
structures at z~3 contain the chemical products from <13 (2 sigma) Population
III enriched minihaloes. The inferred IMF is consistent with that of a Salpeter
distribution and there is a preference towards ejecta from minimally mixed
hypernovae. However, the estimated enrichment model is sensitive to small
changes in the stellar sample. An offset of ~0.1 dex in the [Mg/Ca] abundance
is shown to be sensitive to the inferred number of enriching stars. We suggest
that this method has the potential to constrain the multiplicity of the first
generation of stars, but this will require: (1) a stellar sample whose
systematic errors are well understood; and, (2) documented uncertainties
associated with nucleosynthetic yields.
