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We present the first detailed elemental abundances in the ultra-faintMagellanic satellite galaxies Carina II (Car II) and Carina III (Car III). Withhigh-resolution Magellan/MIKE spectroscopy, we determined abundances of ninestars in Car II including the first abundances of an RR Lyrae star in anultra-faint dwarf galaxy; and two stars in Car III. The chemical abundancesdemonstrate that both systems are clearly galaxies and not globular clusters.The stars in these galaxies mostly display abundance trends matching those ofother similarly faint dwarf galaxies: enhanced but declining [alpha/Fe] ratios,iron-peak elements matching the stellar halo, and unusually low neutron-captureelement abundances. One star displays a low outlying [Sc/Fe] = -1.0. We detecta large Ba scatter in Car II, likely due to inhomogeneous enrichment bylow-mass AGB star winds. The most striking abundance trend is for [Mg/Ca] inCar II, which decreases from +0.4 to -0.4 and indicates clear variation in theinitial progenitor masses of enriching core-collapse supernovae. So far, theonly ultra-faint dwarf galaxies displaying a similar [Mg/Ca] trend are likelysatellites of the Large Magellanic Cloud. We find two stars with [Fe/H] < -3.5,whose abundances likely trace the first generation of metal-free Population IIIstars and are well-fit by Population III core-collapse supernova yields. Anappendix describes our new abundance uncertainty analysis that propagatesline-by-line stellar parameter uncertainties.

Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III