All Figures

$\begin{figure} \par\includegraphics[width=15cm]{11126fig1.ps} \end{figure}$ Figure 1: The two Ca X emission lines discovered in KPD 0005+5106 (thin graphs). Overplotted is the spectrum from a model with $T{\rm\hspace *{-0.4ex}_{eff}}$ = 200 000 K, $\log~g$ = 6.2, and solar Ca abundance. The model was convolved with a Gaussian with ${\it FWHM}=0.05$ Å in order to match the instrumental resolution.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm]{11126fig2.ps} \end{figure}$ Figure 2: Grotrian diagram of our Ca X model ion. Lines discussed in the text are caused by transitions between n=4sublevels. The 4p-4d transition causes the observed UV emission lines.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm]{11126fig3.ps} \end{figure}$ Figure 3: The two Ca X emission lines discovered in KPD 0005+5106 (top spectra) are also seen in the [WCE] central star NGC 2371. The model profiles are the same as in Fig. 1. No attempt is made to fit the possibly wind-contaminated [WCE] profiles. For clarity, the FUSE spectra were smoothed with Gaussians ( FWHM 0.05 and 0.1 Å, respectively). The model spectra (thick lines) were convolved with 0.1 Å Gaussians.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm]{11126fig4.ps} \end{figure}$ Figure 4: HST/STIS spectrum of the PG 1159-type central star NGC 246 and computed profiles for the 4s-4p doublet of Ca X. Their shape reflects the stellar rotation of v sin i = 70 km s^-1. The observation was smoothed with a Gaussian with ${\it FWHM}=0.03$ Å.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm]{11126fig5.ps} \end{figure}$ Figure 5: Ionization fraction of calcium as a function of atmospheric depth in the model with $T{\rm\hspace *{-0.4ex}_{eff}}$ = 200 000 K, $\log~g$ = 6.2, and solar Ca abundance.
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In the text

$\begin{figure} \par\includegraphics[width=9cm]{11126fig6.ps} \end{figure}$ Figure 6: Left: departure coefficients $b_{\rm i}$ for the 4p and 4d levels that cause the Ca X emission lines. Right: ratio of 4p-4d line source function $S_{\rm l}$ to Planck function $B_\nu$ at line centre. The thick horizontal lines near $\log ~ m=0$ denote the line formation region. Dashed lines correspond to the LTE case (b_i=1 and $S_{l}/B_\nu =1$ ). Model parameters as in Fig. 5.
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In the text

$\begin{figure} \par\includegraphics[width=9cm]{11126fig7.ps} \end{figure}$ Figure 7: Profile shapes of the Ca X $\lambda \lambda$ 1137, 1159 Å lines as a function of $T{\rm _{eff}}$ , $\log~g$ , and Ca abundance, as given by the labels.
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In the text

$\begin{figure} \par\includegraphics[width=15cm]{11126fig1.ps} \end{figure}$	Figure 1: The two Ca X emission lines discovered in KPD 0005+5106 (thin graphs). Overplotted is the spectrum from a model with $T{\rm\hspace *{-0.4ex}_{eff}}$ = 200 000 K, $\log~g$ = 6.2, and solar Ca abundance. The model was convolved with a Gaussian with ${\it FWHM}=0.05$ Å in order to match the instrumental resolution.
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$\begin{figure} \par\includegraphics[width=8.5cm]{11126fig2.ps} \end{figure}$	Figure 2: Grotrian diagram of our Ca X model ion. Lines discussed in the text are caused by transitions between n=4sublevels. The 4p-4d transition causes the observed UV emission lines.
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$\begin{figure} \par\includegraphics[width=8.5cm]{11126fig4.ps} \end{figure}$	Figure 4: HST/STIS spectrum of the PG 1159-type central star NGC 246 and computed profiles for the 4s-4p doublet of Ca X. Their shape reflects the stellar rotation of v sin i = 70 km s^-1. The observation was smoothed with a Gaussian with ${\it FWHM}=0.03$ Å.
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$\begin{figure} \par\includegraphics[width=8.5cm]{11126fig5.ps} \end{figure}$	Figure 5: Ionization fraction of calcium as a function of atmospheric depth in the model with $T{\rm\hspace *{-0.4ex}_{eff}}$ = 200 000 K, $\log~g$ = 6.2, and solar Ca abundance.
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$\begin{figure} \par\includegraphics[width=9cm]{11126fig6.ps} \end{figure}$	Figure 6: Left: departure coefficients $b_{\rm i}$ for the 4p and 4d levels that cause the Ca X emission lines. Right: ratio of 4p-4d line source function $S_{\rm l}$ to Planck function $B_\nu$ at line centre. The thick horizontal lines near $\log ~ m=0$ denote the line formation region. Dashed lines correspond to the LTE case (b_i=1 and $S_{l}/B_\nu =1$ ). Model parameters as in Fig. 5.
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$\begin{figure} \par\includegraphics[width=9cm]{11126fig7.ps} \end{figure}$	Figure 7: Profile shapes of the Ca X $\lambda \lambda$ 1137, 1159 Å lines as a function of $T{\rm _{eff}}$ , $\log~g$ , and Ca abundance, as given by the labels.
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