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Past studies based on optical spectroscopy suggest that the five $\omega$ Cenpulsators form a rather homogeneous group of hydrogen-rich subdwarf O starswith effective temperatures of around 50 000 K. This places the stars below thered edge of the theoretical instability strip in the log $g$ $-$ Teff diagram,where no pulsation modes are predicted to be excited. Our goal is to determinewhether this temperature discrepancy is real, or whether the stars' effectivetemperatures were simply underestimated. We present a spectral analysis of tworapidly pulsating extreme horizontal branch (EHB) stars found in $\omega$ Cen.We obtained Hubble Space Telescope/COS UV spectra of two $\omega$ Cenpulsators, V1 and V5, and used the ionisation equilibrium of UV metallic linesto better constrain their effective temperatures. As a by-product we alsoobtained FUV lightcurves of the two pulsators. Using the relative strength ofthe N IV and N V lines as a temperature indicator yields Teff values close to60 000 K, significantly hotter than the temperatures previously derived. Fromthe FUV light curves we were able to confirm the main pulsation periods knownfrom optical data. With the UV spectra indicating higher effective temperaturesthan previously assumed, the sdO stars would now be found within the predictedinstability strip. Such higher temperatures also provide consistentspectroscopic masses for both the cool and hot EHB stars of our previouslystudied sample.

Just how hot are the $\omega$ Centauri extreme horizontal branch pulsators?