Where are the Low-Mass Population III Stars ?
  We study the number and the distribution of low mass Pop III stars in the
Milky Way. In our numerical model, hierarchical formation of dark matter
minihalos and Milky Way sized halos are followed by a high resolution
cosmological simulation. We model the Pop III formation in H2 cooling minihalos
without metal under UV radiation of the Lyman-Werner bands. Assuming a Kroupa
IMF from 0.15 to 1.0 Msun for low mass Pop III stars, as a working hypothesis,
we try to constrain the theoretical models in reverse by current and future
observations. We find that the survivors tend to concentrate on the center of
halo and subhalos. We also evaluate the observability of Pop III survivors in
the Milky Way and dwarf galaxies, and constraints on the number of Pop III
survivors per minihalo. The higher latitude fields require lower sample sizes
because of the high number density of stars in the galactic disk, the required
sample sizes are comparable in the high and middle latitude fields by
photometrically selecting low metallicity stars with optimized narrow band
filters, and the required number of dwarf galaxies to find one Pop III survivor
is less than ten at <100 kpc for the tip of redgiant stars. Provided that
available observations have not detected any survivors, the formation models of
low mass Pop III stars with more than ten stars per minihalo are already
excluded. Furthermore, we discuss the way to constrain the IMF of Pop III star
at a high mass range of > 10 Msun.
