Abstract

IUE observations of the spectroscopic binary HD 698 show that its continuous spectrum corresponds to that of a B5 III-II object and that, even in the ultraviolet, the object is single-lined. The spectrum displays several sets of lines, all in absorption, where we distinguish features that partake of the orbital motion of the B5 component, lines that suggest the existence of nonthermal sources of energy, and lines that form at the boundary of the circumstellar envelope, part of them being of purely interstellar origin. The circumbinary envelope appears to expand and then starts decelerating before we reach the layer where the resonance doublet of Si IV originates. The "discrete absorptions" that are characteristics of the spectra of early-type stars are present in the spectrum. New values of the orbital period and of the rest of the orbital parameters are determined on the basis of all the available ground-based data.