Extended Variability of the Symbiotic Star AG Draconis

Abstract

High and low resolution IUE satellite observations of the symbiotic star AG Draconis covering the period 1979-1989 are presented, and the far-UV spectra are studied. Two extended outburst events are found to have two maxima separated by about 1600 days, a time scale not known to be associated with the star but which is about three times the binary period of the star. Semiforbidden O IV 1397-1407 emission lines intensities imply an electron density from 10 exp 10 to 10 exp 11/cu cm. The line-emitting region is found to have a linear size from 10 exp 12 to 10 exp 13 cm. The He II 1640 A Zanstra method yields T(*) = 87,000 K or greater for the hot component. The time evolution of calculated ionic abundances shows the presence of abundance peaks coincident with the outburst events and the binary phases favoring episodic mass transfers onto the compact star.