2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/10286We present the EUV fluxes derived from the recent "combined stellar structure and atmosphere models" (CoStar models). The atmosphere models in particular account for the stellar wind and include non-LTE effects and line blanketing. We provide an extensive set of calculations from tracks between 20 and 120 Msun at Z=0.02 (solar metallicity) and Z=0.004. They cover the entire parameter space of O3--B0 stars of all luminosity classes. Model uncertainties are discussed in the light of recent EUV and X-ray observations. We show the importance of using adequate O star ionising fluxes for the interpretation of HII regions, young starbursts and related objects.To appear in "From Stars to Galaxies", ASP Conf. Series, Eds. C. Leitherer, U. Fritze-von Alvensleben, J. Huchra uuencoded, compressed Postscript file including all figuresAstrophysicstext