We present detailed chemical element abundance ratios of 17 elements with 8 \leq Z \leq 60 in three metal poor stars in the Ursa Minor dwarf spheroidal galaxy , which we combine with extant data from the literature to assess the predictions of a novel suite of galaxy chemical evolution models .
The spectroscopic data were obtained with the Keck/HIRES instrument and revealed low metallicities of [ Fe / H ] = - 2.12 , - 2.13 and - 2.67 dex .
While the most metal poor star in our sample shows an overabundance of [ Mn/Fe ] and other Fe-peak elements , our overall findings are in agreement with previous studies of this galaxy : elevated values of the [ \alpha /Fe ] ratios that are similar to , or only slightly lower than , the halo values but with SN Ia enrichment at very low metallicity , as well as an enhancement of the ratio of first to second peak neutron capture elements [ Y/Ba ] with decreasing metallicity .
The chemical evolution models which were tailored to reproduce the metallicity distribution function of the dSph , indicate that UMi had an extended star formation which lasted nearly 5 Gyr with low efficiency and are able to explain the [ Y/Ba ] enhancement at low metallicity for the first time .
In particular , we show that the present day lack of gas is probably due to continuous loss of gas from the system , which we model as winds .