  The stellar initial mass function (IMF), along with the star formation rate,
is one of the fundamental properties that any theory of star formation must
explain. An interesting feature of the IMF is that it appears to be remarkably
universal across a wide range of environments. Particularly, there appears to
be little variation in either the characteristic mass of the IMF or its
high-mass tail between clusters with different metallicities. Previous attempts
to understand this apparent independence of metallicity have not accounted for
radiation feedback from high-mass protostars, which can dominate the energy
balance of the gas in star-forming regions. We extend this work, showing that
the fragmentation of molecular gas should depend only weakly on the amount of
dust present, even when the primary heating source is radiation from massive
protostars. First, we report a series of core collapse simulations using the
ORION AMR code that systematically vary the dust opacity and show explicitly
that this has little effect on the temperature or fragmentation of the gas.
Then, we provide an analytic argument for why the IMF varies so little in
observed star clusters, even as the metallicity varies by a factor of 100.
