Contribution of type Ia supernovae to the chemical enrichment of the
  ultra-faint dwarf galaxy Bootes I
  For three stars in the ultra-faint dwarf (UFD) galaxy Bootes I we have
determined the atmospheric parameters, performed a new reduction of
high-resolution spectra from the Subaru archive, and derived the abundances of
eight chemical elements without using the LTE assumption. As a result, among
the galaxies of its class Bootes I now has the largest sample of stars (11)
with a homogeneous set of atmospheric parameters and chemical abundances, and
this makes it the most promising for studying the chemical evolution of UFD
galaxies. We show that in the range -3<[Fe/H]<-2 for each of the three
$\alpha$--process elements, magnesium, calcium, and titanium, a transition from
their overabundance relative to iron with [$\alpha$/Fe]$\approx$0.3 to the
solar [$\alpha$/Fe] ratio occurs. This most likely suggests the commenced
production of iron in type Ia supernovae. The behaviour of the carbon, sodium,
nickel, and barium abundances does not differ from that in more massive
galaxies, our Galaxy and classical dwarf spheroidal galaxies.
