Ultraviolet spectral morphology of the O stars. IV. The OB supergiantsequence.

Abstract

An atlas of 25 O3 - B8 supergiant spectra in the wavelength ranges 1320 Å - 1580 Å and 1620 Å - 1880 Å is presented, based on high-resolution data from the International Ultraviolet Explorer archives. This remarkably detailed relationship between the stellar-wind profiles and the optical spectral classifications throughout this sequence is emphasized. For instance, the Si IV/C IV ratio reverses between O4 and O6.5; and the B0, B0.5, and B0.7 Ia wind characteristics are each qualitatively unique and distinct from one another. The systematic behaviour of nine stellar-wind features with ionization potentials ranging from 114 to 19 eV is summarized as a function of advancing spectral type.