Temporal variations of FeII fluorescence lines in the symbiotic star AG peg

Abstract:
An investigation of Fe II fluorescence by PAR (photoexcitation by accidental resonance) in AG Peg has been carried out using spectra recorded by the IUE satellite. Over 30 active pumping channels caused by PAR are observed and provide an explanation for 180 of the ultraviolet Fe II lines identified in the IUE spectra. The pumping lines are strong nebular lines originating from ionized elements, such as [Si III] lambda1892.03, N IV lambda1718.55, [O IV] lambda1401.16 in the wavelength region from 900 to 2000 Angstrom. In the first IUE spectra (1978) some of the pumping nebular lines had a broad foot at the base, but during the years 1980 to 1990 this declined and became too weak to be observed. During the same years the Fe II fluorescence lines that corresponded to channels at wavelengths remarkably different from their pumping lines vanished since those channels could only be pumped by the broad foot.