The UV silicon spectra of early B stars

Equivalent widths of UV silicon lines obtained from high dispersion IUE SWP spectra for a sample of 37 mid- to early B stars are presented. These are compared to other atmospheric diagnostics and to model atmosphere calculations. It is found that some of the UV silicon lines are extremely sensitive to stellar temperature and luminosity over the range B5-B0.5, or roughly a factor of two in effective temperature. The potential usefulness of these lines is stressed, and it is demonstrated that they could determine temperatures and surface gravities to the same accuracy as other commonly used diagnostics once adequate models become available. Although the available models fail to predict the quantitative behavior of the line strengths, they do, in most instances, describe their qualitative behavior. Since the existing models are somewhat out of date, the results suggest that models based upon more complete opacity tables may be quite reliable.