We have analyzed the complete set of available IUE (International Ultraviolet Explorer) spectra for the symbiotic star AG Draconis covering the period from 1979 to 1989. All absolute line fluxes and wavelengths have been obtained for the prominent emission lines in the λλ1200-3200 wavelength range. These spectra contain observations which were taken before, during and after the two extended outbursts which occurred on 1980 November to 1981 November and 1985 February to 1986 January. These two outburst events have two maxima that are separated by ~1600 days, a time scale not known to be associated with the star, but which is ~3 times the binary period of the star. 0 IV] λλ1397-1407 emission line intensities imply an electron density in the range 10^10 ≤ ne ≤ 10^11 cm^-3. We found the line-emitting region to have a linear size 10^12 ≤ L ≤ 10^13 cm. The He II A1640 Zanstra method yields T ≥ 87,000 K for the hot component. Absolute line intensities are plotted as a function of Julian Date for the principal emission lines of N v λλ1238, 1242,0 I λλ1302-1306, 0 IV] λλ1397-1407, C IV λλ1548, 1550, He II A1640 and 0 m] λλ1660, 1666 to observe the temporal variability of AG Dra. Emission line fluxes of N v, 0 1, N IV], C IV, and N III] are plotted as a function of C IV to study the nature of the emitting regions. We have calculated the nitrogen ionic abundances for AG Dra to study how the ionization levels change during outburst and quiescence phases of the star. The time-evolution of the 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. Monitoring, preferably every 3 to 4 years could be helpful in confirming the accretion-powered outburst mechanism of this star and provide important insights into the symbiotic phenomenon in general.
Kafatos, M., Meier, S.R. (1993) Extended Variability of the Symbiotic Star AG Draconis, Astrophysical Journal Supplement Series, 8:201-214. doi: 10.1086/191751