Observations of narrow absorption components in the ultraviolet spectrum of Zeta Ophiuchi

Abstract

We present 33 high resolution IUE observations of ζ Oph, taken between 1978 and 1981. Narrow absorption components due to resonance transitions of C IV and N V are present in all spectra, Doppler shifted by −1385 km s−1. Examination of previous observations shows these features to have been present for at least 12 years. A much weaker, but also long-lived, set of components is observed at –1250 km s−1. Significant changes in the narrow components accompanied an Hα emission episode. Profile fitting has been used to estimate the column densities of material responsible for the narrow components and for the ‘underlying’ P Cygni profiles. The results are discussed in the context of possible models for the formation of the narrow components. No currently available model appears entirely capable of explaining the observations satisfactorily.