2-DIMENSIONAL ULTRAVIOLET SPECTRAL TYPING OF O-TYPE STARS

We present equivalent-width measurements of ultraviolet photospheric l ines that are useful as spectral type criteria; these include 23 lines of He II, C III, N III, N IV, O IV, Si III, Si IV, S V, Fe IV, and Fe V in IUE spectra of 67 O3 to B0 stars of all luminosity classes. Seve n lines and two line ratios are particularly sensitive to spectral typ e, and we show how the ultraviolet spectral typing diagnostics lead to types that are consistent with optical types. There are few luminosit y-sensitive photospheric lines in the ultraviolet but we find that the N IV lambda 1718 line does have a significant luminosity variation am ong most O subtypes. This criterion leads to ultraviolet classes that are approximately in agreement with optical luminosity classes. This s cheme was developed in order to estimate the spectral types and lumino sity classes of tomographically separated component spectra of O-type binary systems.