Abstract

Star-forming dwarf galaxies in the local Universe represent a unique laboratory for the study of metal-poor massive star populations and a fundamental anchor for stellar models applied across cosmic time. With JWST poised to open a new window onto the rest-ultraviolet light of primordial galaxies in the reionization era and beyond, and with our premier source of local ultraviolet spectra sadly approaching its retirement, confronting models for massive stars with high-quality local observations is of paramount importance. In this talk, I will present results from several HST campaigns which have obtained ultraviolet spectra probing simultaneously both stellar continuum light and the hot nebular gas ionized by these same stars. I will argue that the long-mysterious He II line, which appears both in gas and stellar wind emission, may actually be a powerful probe of some of the most uncertain products of massive star evolution. Finally, I will preview several large UV programs and smaller-scale optical campaigns which chart a path towards calibrating stellar population models in the uncertain metallicity regime that JWST data will routinely rely upon.