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Published online by Cambridge University Press: 03 August 2017
We present direct observational evidence showing that early type WR stars, and WO stars in particular, are exceedingly hot, and that their ionizing radiation is not fully trapped by their extended atmospheres. We show that extreme WR stars, or Warmers, are found in metal poor as well as in metal rich regions in accordance with theory. Images of HeIII regions around Galactic and Magellanic Cloud Warmers are shown.