New Observational Insights into the Astrophysics of Extremely Metal-Poor O Stars
Dr. Grace Telford
Department of Physics and Astronomy
Low-metallicity massive stars shape the evolution of dwarf galaxies and likely powered cosmic reionization. However, observations of individual O stars more metal-poor than the Small Magellanic Cloud (20% solar metallicity) are extremely rare, leaving models that predict their energetic feedback and ionizing fluxes highly uncertain. I will present HST/COS far-ultraviolet spectra of three main-sequence O stars in extremely low-metallicity (3-14% solar) galaxies near the edge of the Local Group. These data reveal that the two most metal-poor stars are both fast rotators (vsin(i) > 290 km/s) driving weak stellar winds, suggesting high ionizing photon production. I will then present Keck/KCWI optical spectroscopy of the HII region ionized by the only O star in the 3% solar metallicity galaxy Leo P. The observed nebular emission tightly constrains the shape and normalization of the stellar ionizing spectrum, enabling a first test of purely theoretical ionizing spectral models at such low metallicity. These new observations provide a much-needed benchmark for the stellar models that are widely used to interpret observations of dwarf galaxies and to measure the contribution of metal-poor galaxies to reionization in the early universe.
Hosted by Prof. Kirby