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M. S. Oey (Lowell Observatory)
The Simple Inhomogeneous Model (SIM) for Galactic chemical evolution suggests a different interpretation of the metallicity distribution function (MDF) for the Galactic halo that contrasts with the homogeneous Simple Model. While the Simple Model for the halo is consistent with a highly evolved system, the SIM shows an extremely unevolved system that remains strongly dominated by stochastic contamination events. The SIM also shows an evolutionary sequence between stars kinematically associated with the ``high halo" and "low halo" populations. This suggests that the high halo and low halo may not necessarily have physically distinct origins.
Since the SIM is driven by stochastic processes, it also provides straightforward predictions for the fraction of zero-metallicity Population~III stars. These are compared to the current observed upper limit, showing an unambiguous discrepancy of at least an order of magnitude between the observed and predicted fraction of Population~III stars for the Galactic halo.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.