IUE observations of CI Cygni during 1979–1981

Extract

High and low resolution IUE spectra of CI Cyg were obtained at VTLSPA during 1979-81 allowing for an analysis of the spectral variations related to the decreasing activity of the star, and to the eclipse (June 1980).

In the high resolution spectra the emission lines have a width slightly larger than the instrumental one. This fact is particularly evident in the HeII 1640 A line and could be related to the peculiar behaviour of this line at low resolution as reported by Michalitsianos et al. (this volume). A systematic radial velocity difference between permitted and intercombination lines was found; this difference should be connected with the structure of the emitting region(s). “Secular” and eclipse varia tion was found in particular in the intercombination line intensities (Viotti et al. 1980). An electron density of ∼ 0.3–1.5×10¹⁰ cm^–3 was evaluated from the intensity ratios of the NIII] emission lines. No significant difference in these ratios and in the CIII]/NIII] ratio as well was found,during 1979, 1980 (eclipse) and 1981 suggesting no large N_e variation with both the activity phase and eclipse of the star. This result should imply a low density gradient in the partially eclipsed NIII] and CIII] regions. A more detailed analysis of the high resolution data is in course to better clearfy these points, and their implications on the possible models for CI Cyg.