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Metal-poor massive stars dominate the light we observe from star-formingdwarf galaxies and may have produced the bulk of energetic photons thatreionized the universe at high redshift. Yet, the rarity of observations ofindividual O stars below the $20\%$ solar metallicity ($Z_\odot$) of the SmallMagellanic Cloud (SMC) hampers our ability to model the ionizing fluxes ofmetal-poor stellar populations. We present new Hubble Space Telescopefar-ultraviolet (FUV) spectra of three O-dwarf stars in the galaxies Leo P($3\%\,Z_\odot$), Sextans A ($6\%\,Z_\odot$), and WLM ($14\%\,Z_\odot$). Wequantify equivalent widths of photospheric metal lines and strengths ofwind-sensitive features, confirming that both correlate with metallicity. Weinfer the stars' fundamental properties by modeling their FUV throughnear-infrared spectral energy distributions and identify stars in the SMC withsimilar properties to each of our targets. Comparing to the FUV spectra of theSMC analogs suggests that (1) the star in WLM has an SMC-like metallicity, and(2) the most metal-poor star in Leo P is driving a much weaker stellar windthan its SMC counterparts. We measure projected rotation speeds and find thatthe two most metal-poor stars have high $v\,\mathrm{sin}(i)\,\geq\,290\,\mathrm{km}\,\mathrm{s}^{-1}$, and estimate justa $3-6\%$ probability of finding two fast rotators if the metal-poor stars aredrawn from the same $v \,\mathrm{sin}(i)$ distribution observed for O dwarfs inthe SMC. These observations suggest that models should include the impact ofrotation and weak winds on ionizing flux to accurately interpret observationsof metal-poor galaxies in both the near and distant universe.

Far-Ultraviolet Spectra of Main-Sequence O Stars at Extremely Low Metallicity