All Figures

$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig1.eps}\end{figure}$ Figure 1: The normalized growth rate in terms of period (in seconds) for overstable g-modes corresponding to two $0.589~M_{\odot}$ PG 1159 models. The location of these models on the HR diagram is shown in Fig. 3. The circumscribed dot in panel a) corresponds to a mode with k= 70.
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In the text

$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig2.eps}\end{figure}$ Figure 2: The opacity and opacity derivatives ( left scale), and the differential work function ( right scale) for two selected $\ell = 1$ modes in terms of the mass coordinate ( lower scale) and the logarithm of the temperature ( upper scale), corresponding to the PG 1159 model (a) analyzed in Fig. 1. ${\rm d}W/{\rm d}r$ for the mode with k=70 (k= 150) is normalized to an extremum value of +1 (-1). The vertical dot-dashed line shows the location of the maximum in the C/O opacity bump.
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In the text

$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig3.eps}\end{figure}$ Figure 3: The HR diagram for our complete set of PG 1159 model sequences of 0.530, 0.542, 0.565, 0.589, 0.609, 0.664 and $0.741~M_{\odot}$ ( from right to left). The portions of the tracks harbouring stellar models with overstable $\ell = 1$ g-modes are emphasized with thick solid lines. Thin dashed ( $\ell = 1$ ) and dotted ( $\ell = 2$ ) lines are parameterizations of the blue and red edges of instability. The small white circles on the $0.589~M_{\odot}$ track show the loci of the two template models analyzed in Fig. 1.
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In the text

$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig4.eps}\end{figure}$ Figure 4: Same as Fig. 3, but for the $\log (T_{\rm eff}) - \log g$ plane.
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In the text

$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig5.eps}\end{figure}$ Figure 5: The instability domains on the $\log(T_{\rm eff})-\Pi$ plane for g-modes with $\ell = 1$ corresponding to our complete set of PG 1159 model sequences. Different line styles depict the situation for different stellar masses.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{5423fig6.eps}\end{figure}$ Figure 6: The distribution of the spectroscopically calibrated variable and non-variable PG 1159 stars in the $\log (T_{\rm eff}) - \log g$ plane. PG 1159 stars with no variability data (N.V.D.) are depicted with hollow symbols. Solid curves show the evolutionary tracks for different stellar masses: 0.530, 0.542, 0.565, 0.589, 0.609, 0.664 and $0.741~M_{\odot}$ . Parameterizations of the theoretical dipole (dashed curves) and quadrupole (dotted curves) red and blue edges of the instability domain are also displayed.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{5423fig7.eps}\end{figure}$ Figure 7: The period ranges of known variable PG 1159 stars on the $\log(T_{\rm eff})-\Pi$ plane, depicted with thick vertical bars (the thickness of the bars is arbitrary). For comparison, we include the predicted ranges of unstable periods according to Quirion et al. (2004), shown with thinner vertical bars (arbitrarily shifted to the right for clarity). The theoretical instability domains for g-modes with $\ell = 1$ for our complete set of PG 1159 sequences are depicted with different line styles.
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In the text

$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig1.eps}\end{figure}$	Figure 1: The normalized growth rate in terms of period (in seconds) for overstable g-modes corresponding to two $0.589~M_{\odot}$ PG 1159 models. The location of these models on the HR diagram is shown in Fig. 3. The circumscribed dot in panel a) corresponds to a mode with k= 70.
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$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig4.eps}\end{figure}$	Figure 4: Same as Fig. 3, but for the $\log (T_{\rm eff}) - \log g$ plane.
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$\begin{figure} \par\includegraphics[width=8.15cm,clip]{5423fig5.eps}\end{figure}$	Figure 5: The instability domains on the $\log(T_{\rm eff})-\Pi$ plane for g-modes with $\ell = 1$ corresponding to our complete set of PG 1159 model sequences. Different line styles depict the situation for different stellar masses.
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