A Library of Theoretical Ultraviolet Spectra of Massive, Hot Stars for
  Evolutionary Synthesis
  We computed a comprehensive set of theoretical ultraviolet spectra of hot,
massive stars with the radiation-hydrodynamics code WM-Basic. This model
atmosphere and spectral synthesis code is optimized for computing the strong P
Cygni-type lines originating in the winds of hot stars, which are the strongest
features in the ultraviolet spectral region. The computed set is suitable as a
spectral library for inclusion in evolutionary synthesis models of star
clusters and star-forming galaxies. The chosen stellar parameters cover the
upper left Hertzsprung-Russell diagram at L >~ 10^2.75 Lsun and T_eff >~ 20,000
K. The adopted elemental abundances are 0.05 Zsun, 0.2 Zsun, 0.4 Zsun, Zsun,
and 2 Zsun. The spectra cover the wavelength range from 900 to 3000 {\AA} and
have a resolution of 0.4 {\AA}. We compared the theoretical spectra to data of
individual hot stars in the Galaxy and the Magellanic Clouds obtained with the
International Ultraviolet Explorer (IUE) and Far Ultraviolet Spectroscopic
Explorer (FUSE) satellites and found very good agreement. We built a library
with the set of spectra and implemented it into the evolutionary synthesis code
Starburst99 where it complements and extends the existing empirical library
towards lower chemical abundances. Comparison of population synthesis models at
solar and near-solar composition demonstrates consistency between synthetic
spectra generated with either library. We discuss the potential of the new
library for the interpretation of the rest-frame ultraviolet spectra of
star-forming galaxies. Properties that can be addressed with the models include
ages, initial mass function, and heavy-element abundance. The library can be
obtained both individually or as part of the Starburst99 package.
