On the Interpretation of the Ultraviolet Spectra of Symbiotic Stars and Recurrent Novae. I.

Abstract

We present an analysis of high-resolution spectra of several symbiotics and symbiotic novae. We show that the emission lines are severely affected by differential extinction caused by absorption lines in the wind of the red giant companion. The major source of the absorbing spectrum is the forest of lines produced by neutral and singly ionized iron peak elements. We present models for the effects of this "iron curtain," and we show that some of the outstanding anomalies in the emission-line fluxes results from the differential absorption by the environment as the path length along the line-of-sight changes; (2) observed ultraviolet continuum temperatures should, in general, be considerably lower than that inferred from the Zanstra method or related measures of the ionization temperature; (3) disappearance of the emission lines need not imply any changes at all in the intrinsic properties of the ionizing source but may simply reflect the orbital modulation of its intensity by the circumstellar environment; (4) circumstellar absorption also affects the interpretation of broad emission line profiles; and (5) the absence of emission lines is not a strong argument against the existence of an accretion disk around the hot component.