Ionizing photon emission rates from O- and early B-type stars and clusters

We present new computations of the ionizing spectral energy distributions (SEDs), and Lyman continuum (Lyc) and He I continuum photon emission rates, for hot O-type and early B-type stars. We consider solar-metallicity stars, with effective temperatures ranging from 25,000 to 55,000 K and surface gravities (cm s(-2)) log g ranging from 3 to 4, covering the full range of spectral types and luminosity classes for hot stars. We use our updated (WM-basic) code to construct radiation-driven wind atmosphere models for hot stars. Our models include the coupled effects of hydrodynamics and non-LTE radiative transfer in spherically out. owing winds, including the detailed effects of metal line blocking and line blanketing on the radiative transfer and energy balance. Our grid of model atmospheres is available on the World Wide Web. We incorporate our hot-star models into our population synthesis code (STARS), and we compute the time-dependent SEDs and resulting Lyc and He I emission rates for evolving star clusters. We present results for continuous and impulsive star formation for a range of assumed stellar initial mass functions.