All Figures

$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{3396fi1.eps} \end{figure}$ Figure 1: The dots represent the noise level for each of the different orders in the longest exposed IUE spectra, LWP25995 and SWP47715. The lines represent the noise level in the ${\it HST}$ and ${\it FUSE}$ spectra used in this work. The y-axis gives the value of the logarithm of the noise level measured in erg cm^-2 s^-1 Å^-1. The noise level is defined as twice the standard deviation of the pixel intensity from the mean intensity, measured in wavelength regions not affected by spectral lines.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.5cm,clip]{3396fi2a.ps}\hspace*{2mm} \includegraphics[angle=90,width=7.5cm,clip]{3396fi2b.ps} \end{figure}$ Figure 2: The development of He II Balmer $\alpha$ . The spectrum to the left (SWP02326) was recorded in 1978 and the spectrum to the right (SWP40148) was recorded in 1990. The large change in profile width is related to the change in origin for He II emission between those dates. In 1978 most of the He II emission originated from the white-dwarf wind while in 1990 the emission instead came from the heated part of the extended red-giant atmosphere.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=90,width=7cm,clip]{3396fi3a.ps}\hspace*{2mm} \includegraphics[angle=90,width=7cm,clip]{3396fi3b.ps} \end{figure}$ Figure 3: The IUE spectrum (SWP02334) of AG Peg, recorded in 1978, illustrates the difference in the profiles between lines from ions of ionisation energy near 40 eV and those of higher ionisation energy (around 70 eV). The N IV] $\lambda$ 1486 had a contribution from a "nebular line'' already in 1978 while all flux in the N V resonance doublet came from the white-dwarf wind.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=8cm,clip]{3396fi4.eps} \end{figure}$ Figure 4: The total intensity of all Fe II lines from the upper level y²D_5/2, which is pumped by the C IV $\lambda$ 1548.187 line through the channel a⁴F_7/2-y²D_5/2 at 1548.697 Å. When the broad foot of the C IV resonance lines vanished the activity in this channel stopped.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=8cm,clip]{3396fi5.eps} \end{figure}$ Figure 5: The strength of the $\lambda$ 2508.34 Fe II line representing the channel a⁴D_7/2-(b³F) 4p ⁴G_9/2 pumped by H Ly $\alpha$ . As the temperature increased the H II region around the white dwarf became larger, which allowed more H Ly $\alpha$ to reach the Fe II regions.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3396fi6.eps} \end{figure}$ Figure 6: Grotrian diagram of Fe II showing the levels involved in continuum fluorescence. The dotted lines are the pumped channels while the solid lines represent decay channels observed in AG Peg.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=4.2cm,clip]{3396fi7a.eps}\hspace*{2mm} \includegraphics[width=4.2cm,clip]{3396fi7b.eps} \end{figure}$ Figure 7: Suggestion of the origin of broad He emission ( left) and narrow He emission ( right) before and after 1986 (see text).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.5cm,clip]{3396fi8a.ps}\hspa... ...pace*{2mm} \includegraphics[angle=90,width=7.5cm,clip]{3396fi8f.ps} \end{figure}$ Figure 8: The ns ²S-np ²P doublets observed in AG Peg. The figures represent the profile of the resonance doublets after the transition period in the middle of the 1980s. The resonance doublets corresponding to n = 3 (Si IV, Al III, Mg II) and C IV almost completely consist of narrow components, while the N V and O VI resonance doublets still have detectable contributions from the broad white-dwarf wind profile.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{3396fi9a.ps}\par\includegraphics[angle=90,width=8cm,clip]{3396fi9b.ps} \end{figure}$ Figure 9: The intercombination multiplet 2s²2p ²P-2s2p² ⁴P in N III] and O IV] spectra. The fine-structure component 3/2-5/2 is over-exposed in the N III] plot. The region of the N III] multiplet has not been observed by HST (GHRS) at high resolution. The dynamic range of ${\it IUE}$ was not sufficient to record spectra where the weakest N III] components are observable at the same time that N III] 3/2-5/2 is not over-exposed.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{3396fi10.ps} \end{figure}$ Figure 10: The O I multiplet 2p⁴ ³P-2p³(⁴S)3s ³S. The component ³P₂-³S₁to the ground level is in absorption while the other two fine-structure components are in emission.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3396fi11.eps} \end{figure}$ Figure 11: Figure demonstrating our idea of the excitation mechanism in Fe III and Fe II responsible for the observed octet transitions in Fe II. The presumed recombination channels are presented as dotted lines, the pumped channel as a double lines and the decay channels as solid lines. Only the levels involved in the process are plotted in this Grotrian diagram.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{3396fi12.ps} \end{figure}$ Figure 12: The three O III 2p3p ³S-2p3d ³P transitions in spectrum lwp25995. Whit the dynamical range of IUE it is not sufficient to observe the ³S₁-³P₀ transition without having the ³S₁-³P₂ transition saturated because of the large difference of intensity.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=90,width=7cm,clip]{3396fi3a.ps}\hspace*{2mm} \includegraphics[angle=90,width=7cm,clip]{3396fi3b.ps} \end{figure}$	Figure 3: The IUE spectrum (SWP02334) of AG Peg, recorded in 1978, illustrates the difference in the profiles between lines from ions of ionisation energy near 40 eV and those of higher ionisation energy (around 70 eV). The N IV] $\lambda$ 1486 had a contribution from a "nebular line'' already in 1978 while all flux in the N V resonance doublet came from the white-dwarf wind.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=8cm,clip]{3396fi4.eps} \end{figure}$	Figure 4: The total intensity of all Fe II lines from the upper level y²D_5/2, which is pumped by the C IV $\lambda$ 1548.187 line through the channel a⁴F_7/2-y²D_5/2 at 1548.697 Å. When the broad foot of the C IV resonance lines vanished the activity in this channel stopped.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=8cm,clip]{3396fi5.eps} \end{figure}$	Figure 5: The strength of the $\lambda$ 2508.34 Fe II line representing the channel a⁴D_7/2-(b³F) 4p ⁴G_9/2 pumped by H Ly $\alpha$ . As the temperature increased the H II region around the white dwarf became larger, which allowed more H Ly $\alpha$ to reach the Fe II regions.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3396fi6.eps} \end{figure}$	Figure 6: Grotrian diagram of Fe II showing the levels involved in continuum fluorescence. The dotted lines are the pumped channels while the solid lines represent decay channels observed in AG Peg.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=4.2cm,clip]{3396fi7a.eps}\hspace*{2mm} \includegraphics[width=4.2cm,clip]{3396fi7b.eps} \end{figure}$	Figure 7: Suggestion of the origin of broad He emission ( left) and narrow He emission ( right) before and after 1986 (see text).
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{3396fi10.ps} \end{figure}$	Figure 10: The O I multiplet 2p⁴ ³P-2p³(⁴S)3s ³S. The component ³P₂-³S₁to the ground level is in absorption while the other two fine-structure components are in emission.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=8cm,clip]{3396fi11.eps} \end{figure}$	Figure 11: Figure demonstrating our idea of the excitation mechanism in Fe III and Fe II responsible for the observed octet transitions in Fe II. The presumed recombination channels are presented as dotted lines, the pumped channel as a double lines and the decay channels as solid lines. Only the levels involved in the process are plotted in this Grotrian diagram.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{3396fi12.ps} \end{figure}$	Figure 12: The three O III 2p3p ³S-2p3d ³P transitions in spectrum lwp25995. Whit the dynamical range of IUE it is not sufficient to observe the ³S₁-³P₀ transition without having the ³S₁-³P₂ transition saturated because of the large difference of intensity.
Open with DEXTER