The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D
  abundance analysis. II. Early chemical enrichment
  We present the non-local thermodynamic equilibrium (NLTE) abundances of up to
10 chemical species in a sample of 59 very metal-poor (VMP, -4 < [Fe/H] < -2)
stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW)
halo. Our results are based on high-resolution spectroscopic datasets and
homogeneous and accurate atmospheric parameters determined in PaperI. We show
that once the NLTE effects are properly taken into account, all massive
galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor,
Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [alpha/Fe] ~ 0.3
for each of the alpha-process elements: Mg, Ca, and Ti. We put on a firm ground
the evidence for a decline in alpha/Fe with increasing metallicity in the
BootesI ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta
of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs
reveal indistinguishable trends with metallicity, suggesting that the processes
of Na and Al synthesis are identical in all systems, independent of their mass.
The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical
dSphs, similarly to the MW halo, calling for two different nucleosynthesis
channels for Sr. We show that Sr in the massive galaxies is well correlated
with Mg suggesting a strong link to massive stars and that its production is
essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs:
BootesI, UMaII, and LeoIV are depleted in Sr and Ba relative to Fe and Mg, with
very similar ratios of [Sr/Mg] ~ -1.3 and [Ba/Mg] ~ -1 on the entire range of
their Mg abundances. The subsolar Sr/Ba ratios of Bootes I and UMa II indicate
a common r-process origin of their neutron-capture elements. Sculptor remains
the classical dSph, in which the evidence for inhomogeneous mixing in the early
evolution stage, at [Fe/H] < -2, is the strongest.
