Spectral synthesis in the ultraviolet. I - Far-ultraviolet stellar library

A library of mean stellar energy distributions for use in population synthesis of the ultraviolet spectra of active star-forming galaxies is derived from the ultraviolet spectrophotometry in the IUE Spectral Atlas. The spectra extend from 1230 to 1930 A with a resolution of 6 A. The library contains eight main-sequence groups from O3 to A7 V, four giant groups from O5 to B9 III, and three supergiant groups from O9 to A0 I. Several continuum and spectral line indices are computed, and their usefulness as temperature and luminosity discriminants is discussed. The advantages of analyzing composite stellar populations in the far-ultraviolet, where cool starlight is strongly suppressed, are examined.