Five stars in the extreme outskirts (from ∼ 5 to ∼ 12 elliptical half-light radii, r h ) of the Ursa Minor (UMi) dwarf galaxy have been identified as potential new members using a Bayesian algorithm applied to Gaia EDR3 data. These targets were observed with the GRACES spectrograph, resulting in precise radial velocities and metallicities that confirm their association with UMi. For the brightest and outermost star (Target 1, at ∼ 12 r h ), the chemical abundances of α-(Mg, Ca, Ti), odd-Z (Na, K, Sc), Fe-peak (Fe, Ni, Cr), and neutron-capture process (Ba) elements have also been determined. We also discuss data from the literature and from APOGEE DR17. We find the chemical patterns in UMi are consistent with a star formation history that includes yields from core collapse supernovae, asymptotic giant branch stars, and supernovae Ia. Evidence for a knee in the [α/Fe] ratios near [Fe/H] ∼ −2.1 indicates a low star formation efficiency similar to that in other dwarf galaxies. Given the distance of Target 1 from the centre of UMi (R∼4.5 kpc), we show that UMi has a more extended structure than previously thought. This "stellar halo" around UMi could be a secondary feature resulting from tidal stripping after multiple orbits around the Galaxy, or maybe a primary UMi feature due to early hierarchical accretion activity or to strong gravitational fluctuations prompted by feedback in the early star formation phase. Also consistent with observations is a late-time merger-free scenario where outside-in star formation is accompanied by gradual supernovae Ia enrichment.
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