Are the Formation and Abundances of Metal-Poor Stars the Result of Dust
  Dynamics?
  Large dust grains can fluctuate dramatically in their local density, relative
to gas, in neutral, turbulent disks. Small, high-redshift galaxies (before
reionization) represent ideal environments for this process. We show via simple
arguments and simulations that order-of-magnitude fluctuations are expected in
local abundances of large grains under these conditions. This can have
important consequences for star formation and stellar abundances in extremely
metal-poor stars. Low-mass stars could form in dust-enhanced regions almost
immediately after some dust forms, even if the galaxy-average metallicity is
too low for fragmentation to occur. The abundances of these 'promoted' stars
may contain interesting signatures, as the CNO abundances (concentrated in
large carbonaceous grains and ices) and Mg and Si (in large silicate grains)
can be enhanced or fluctuate independently. Remarkably, otherwise puzzling
abundance patterns of some metal-poor stars can be well-fit by standard
core-collapse SNe yields, if we allow for fluctuating dust-to-gas ratios. We
also show that the observed log-normal-like distribution of enhancements in
these species agrees with our simulations. Moreover, we confirm Mg and Si are
correlated in these stars, with abundance ratios similar to those in local
silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure
SNe yields, shows large enhancements as expected in the dust-promoted model,
preferentially in the [C/Fe]-enhanced metal-poor stars. This suggests that (1)
dust exists in second-generation star formation, (2) dust-to-gas ratio
fluctuations occur and can be important for star formation, and (3) light
element abundances of these stars may be affected by the chemistry of dust
where they formed, rather than directly tracing nucleosynthesis.
