All Figures

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{9111fig1.ps}\end{figure}$ Figure 1: The spectra of NGC 4151 corresponding to the high activity state ( top) and to the low activity state ( bottom). The observed wavelength (we recall that z=0.0033) is displayed on the X-axis, and the flux (in units of 10^-14 erg cm^-2 s^-1 Å^-1) is displayed on the Y-axis.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{9111fig2.eps}\end{figure}$ Figure 2: The light curves of H $\alpha$ , H $\beta$ , H $\gamma$ , HeII $\lambda$ 4686 and of the continuum at the observed wavelength $\lambda =5117$ Å, in the period 1996-2006. Constant contributions from the narrow lines (Table 9) and from of the host galaxy (see Sect. 3.1) are shown by horizontal dashed lines. The line fluxes are given in units of 10 $^{-12}~\rm erg~cm^{-2}~s^{-1}$ , and the continuum flux in units of 10 $^{-14}~\rm erg~cm^{-2}~s^{-1}~\AA^{-1}$ . The horizontal lines in the first panel correspond to the division of the continuum flux into three intervals (see Sect. 3.4.2), and the vertical lines correspond to the division into time intervals based on the similarity of the line shapes (see Sect. 3.3).
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In the text

$\begin{figure} \par\includegraphics[width=15.3cm,clip]{9111fig3.eps}\end{figure}$ Figure 3: The variation of the wings and core of H $\alpha$ ( left) and H $\beta$ ( right) from 1996 to 2006. The flux is given in units of 10 $^{-12}~\rm erg~cm^{-2}~s^{-1}$ .
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In the text

$\begin{figure} \par\includegraphics[width=15.3cm,clip]{9111fig4.eps}\end{figure}$ Figure 4: The variation in the ratio of the fluxes in the line wings and in the core of H $\alpha$ ( left) and H $\beta$ ( right) (see the text), from 1996 to 2006.
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In the text

$\begin{figure} \par\includegraphics[width=3.6cm,clip]{9111fig5a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig5b.ps}\end{figure}$ Figure 5: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the first period.
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In the text

$\begin{figure} \par\includegraphics[width=3.6cm,clip]{9111fig6a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig6b.ps}\end{figure}$ Figure 6: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the second period.
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In the text

$\begin{figure} \par\includegraphics[width=3.5cm,clip]{9111fig7a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig7b.ps}\end{figure}$ Figure 7: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the third period.
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In the text

$\begin{figure} \par\includegraphics[width=3.5cm,clip]{9111fig8a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig8b.ps}\end{figure}$ Figure 8: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the whole monitoring period.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{9111fig9.eps}\end{figure}$ Figure 9: The H $\alpha$ , H $\gamma$ , HeII $\lambda$ 4686 fluxes versus the H $\beta$ flux.The correlation coefficients r are given inside the plot. The flux is given in units of 10^-12 erg cm^-2 s^-1.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{9111fig10.eps}\end{figure}$ Figure 10: The H $\alpha$ , H $\beta$ , H $\gamma$ , HeII $\lambda$ 4686 fluxes versus the continuum flux (at $\lambda =5117$ Å). The correlation coefficients r are given inside the plot. The line fluxes are given in units of 10^-12 erg cm^-2 s^-1, and the continuum flux in units of 10^-14 erg cm^-2 s^-1Å^-1.
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{9111fig11.eps}\end{figure}$ Figure 11: The wings and core fluxes as a function of the continuum flux (at $\lambda =5117$ Å) for H $\alpha$ ( left) and H $\beta$ ( right). The line and continuum fluxes are given in the same units as in Fig. 10.
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{9111fig12.eps}\end{figure}$ Figure 12: H $\alpha$ ( left) and H $\beta$ ( right) fluxes for the three periods (first to third from top to down) as a function of the continuum flux. The line and conntinuum fluxes are given in the same units as in Fig. 10.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{9111fig13.eps} \end{figure}$ Figure 13: Computed H $\beta$ flux at Earth in erg cm^-2 s^-1 for the conditions of NGC 4151, as a function of the density in cm^-3; left, for a column density of 10²⁴ cm^-2, right for 10²³ cm^-2. See the text for more explanations.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{9111fig1.ps}\end{figure}$	Figure 1: The spectra of NGC 4151 corresponding to the high activity state ( top) and to the low activity state ( bottom). The observed wavelength (we recall that z=0.0033) is displayed on the X-axis, and the flux (in units of 10^-14 erg cm^-2 s^-1 Å^-1) is displayed on the Y-axis.
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$\begin{figure} \par\includegraphics[width=15.3cm,clip]{9111fig3.eps}\end{figure}$	Figure 3: The variation of the wings and core of H $\alpha$ ( left) and H $\beta$ ( right) from 1996 to 2006. The flux is given in units of 10 $^{-12}~\rm erg~cm^{-2}~s^{-1}$ .
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$\begin{figure} \par\includegraphics[width=15.3cm,clip]{9111fig4.eps}\end{figure}$	Figure 4: The variation in the ratio of the fluxes in the line wings and in the core of H $\alpha$ ( left) and H $\beta$ ( right) (see the text), from 1996 to 2006.
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$\begin{figure} \par\includegraphics[width=3.6cm,clip]{9111fig5a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig5b.ps}\end{figure}$	Figure 5: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the first period.
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$\begin{figure} \par\includegraphics[width=3.6cm,clip]{9111fig6a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig6b.ps}\end{figure}$	Figure 6: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the second period.
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$\begin{figure} \par\includegraphics[width=3.5cm,clip]{9111fig7a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig7b.ps}\end{figure}$	Figure 7: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the third period.
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$\begin{figure} \par\includegraphics[width=3.5cm,clip]{9111fig8a.ps}\hspace*{4mm} \includegraphics[width=3.5cm,clip]{9111fig8b.ps}\end{figure}$	Figure 8: The averaged and rms profiles of the broad H $\alpha$ ( left) and H $\beta$ ( right) lines for the whole monitoring period.
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$\begin{figure} \par\includegraphics[width=7.5cm,clip]{9111fig9.eps}\end{figure}$	Figure 9: The H $\alpha$ , H $\gamma$ , HeII $\lambda$ 4686 fluxes versus the H $\beta$ flux.The correlation coefficients r are given inside the plot. The flux is given in units of 10^-12 erg cm^-2 s^-1.
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$\begin{figure} \par\includegraphics[width=7.5cm,clip]{9111fig10.eps}\end{figure}$	Figure 10: The H $\alpha$ , H $\beta$ , H $\gamma$ , HeII $\lambda$ 4686 fluxes versus the continuum flux (at $\lambda =5117$ Å). The correlation coefficients r are given inside the plot. The line fluxes are given in units of 10^-12 erg cm^-2 s^-1, and the continuum flux in units of 10^-14 erg cm^-2 s^-1Å^-1.
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$\begin{figure} \par\includegraphics[width=15cm,clip]{9111fig11.eps}\end{figure}$	Figure 11: The wings and core fluxes as a function of the continuum flux (at $\lambda =5117$ Å) for H $\alpha$ ( left) and H $\beta$ ( right). The line and continuum fluxes are given in the same units as in Fig. 10.
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$\begin{figure} \par\includegraphics[width=15cm,clip]{9111fig12.eps}\end{figure}$	Figure 12: H $\alpha$ ( left) and H $\beta$ ( right) fluxes for the three periods (first to third from top to down) as a function of the continuum flux. The line and conntinuum fluxes are given in the same units as in Fig. 10.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{9111fig13.eps} \end{figure}$	Figure 13: Computed H $\beta$ flux at Earth in erg cm^-2 s^-1 for the conditions of NGC 4151, as a function of the density in cm^-3; left, for a column density of 10²⁴ cm^-2, right for 10²³ cm^-2. See the text for more explanations.
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