Can Stellar Yields Accurately Constrain the Upper Limit to the Initial Mass Function?

Recent determinations of the upper mass limit to the local initial mass function (IMF) claim a value of m(upper)=50+/-10 solar masses, based upon direct comparisons of the observed oxygen and iron abundances in metal-poor stars with the predicted stellar yields from Type II supernovae (SNe). An unappreciated uncertainty in these analyses is the input physics intrinsic to each SNe grid, and its effect upon stellar nucleosynthesis. We demonstrate how such uncertainties, coupled with the uncertain metal-poor halo star normalization, while allowing us to set a lower bound to m(upper) of approximately 40 solar masses, nullifies any attempt at constraining the upper bound.