Contribution of Type Ia Supernovae to the Chemical Enrichment of the Ultra-Faint Dwarf Galaxy Boötes I

For three stars in the ultra-faint dwarf (UFD) galaxy Boötes 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 Boötes 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 α-process elements, magnesium, calcium, and titanium, a transition from their overabundance relative to iron with [α/Fe] ∼ 0.3 to the solar [α/Fe] ratio occurs. This most likely suggests the commenced production of iron in type Ia supernovae. The behavior of the carbon, sodium, nickel, and barium abundances does not differ from that in more massive galaxies, our Galaxy and classical dwarf spheroidal galaxies.