IUE Observations of Z Andromedae: Spectral Variations during Quiescence and a Physical Model

Abstract

The authors describe the results of an extensive monitoring of the ultraviolet spectrum of the symbiotic star Z And based on high- and low-resolution IUE observations made during 1978 - 1982, when the star was in a phase of quiescence. Large variations of the Balmer continuum and emission-line intensities where observed on a time scale of about 760 days, with maxima and minima in phase with the UBV and Hα variability. The following spectral components are identified in the UV-to-IR energy spectrum of Z And: (1) a non variable M3.5 giant; (2) a hot source with a temperature ≥10⁵K and a mean radius of 0.07 R_sun;; and (3) a nebular component associated with the hot source. A binary model of Z And with a period of 760 days is presented.