The effects of stellar winds of fast-rotating massive stars in the
  earliest phases of the chemical enrichment of the Galaxy
  We use the growing data sets of very-metal-poor stars to study the impact of
stellar winds of fast rotating massive stars on the chemical enrichment of the
early Galaxy. We use an inhomogeneous chemical evolution model for the Galactic
halo to predict both the mean trend and scatter of C/O and N/O. In one set of
models, we assume that massive stars enrich the interstellar medium during both
the stellar wind and supernovae phases. In the second set, we consider that in
the earliest phases (Z <10^-8), stars with masses above 40 Msun only enrich the
interstellar medium via stellar winds, collapsing directly into black holes. We
predict a larger scatter in the C/O and N/O ratios at low metallicities when
allowing the more massive fast-rotating stars to contribute to the chemical
enrichment only via stellar winds. The latter assumption, combined with the
stochasticity in the star formation process in the primordial Galactic halo can
explain the wide spread observed in the N/O and C/O ratios in normal
very-metal-poor stars. For chemical elements with stellar yields that depend
strongly on initial mass (and rotation) such as C, N, and neutron capture
elements, within the range of massive stars, a large scatter is expected once
the stochastic enrichment of the early interstellar medium is taken into
account. We also find that stellar winds of fast rotators mixed with
interstellar medium gas are not enough to explain the large CNO enhancements
found in most of the carbon-enhanced very-metal-poor stars. In particular, this
is the case of the most metal-poor star known to date, HE 1327-2326, for which
our models predict lower N enhancements than observed when assuming a mixture
of stellar winds and interstellar medium. We suggest that these carbon-enhanced
very metal-poor stars were formed from almost pure stellar wind material,
without dilution with the pristine interstellar medium.
