UV Spectroscopic Dating of Stars and Galaxies

We report on new stellar models and spectral analyses carried out for the purpose of dating high-redshift galaxies from their rest-frame UV spectra. The principle behind UV spectrscopic dating is simple. For passively evolving stellar populations younger than about 7 Gyr, the hottest stars are at the main sequence turnoff (MSTO). These stars are thus the only source of significant flux in the mid-ultraviolet (2000 — 3200 A) spectra of such galaxies; in fact, the spectra are remarkably similar to that of a single F-star. By determining the effective temperature of the MSTO stars, we can measure the age of the population.