All Figures

$\begin{figure} \par\includegraphics[angle=-90,width=7.3cm]{0643fig1.eps}\end{figure}$ Figure 1: The spiral arm definition using the parameters $\theta _{0}$ , the angle between the tangent to the spiral pattern (extrapolated to the disk centre at $R_{\rm spiral}=0 ~R_{L_{1}}$ ) and the line-of-centres, and $\alpha ~ (= \!-180 \hbox{$^\circ$ })$ , the opening angle of the spiral, or the change in angle ( $\theta - \theta _{0}$ ) it takes to go from $R_{\rm spiral}=0$ to $R_{\rm spiral}= R_{L_{1}}$ . The line-of-centres is the positive direction of the x-axis and the angles are measured counter-clockwise.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=14.2cm]{0643fig2.eps}\end{figure}$ Figure 2: A model accretion disk with a spiral structure at different rotation angles and the corresponding total, disk, and spiral light curves. The model surface brightness distributions are shown in a logarithmic grayscale (dark regions are brighter). Dotted lines depict the primary Roche lobe, the gas stream trajetory, and the disk radius at 0.2 and 0.6 R_L₁ (extent of observed spiral shocks; Baptista et al. 2000). A cross marks the disk centre. The stars rotate counter-clockwise and the secondary is to the right of each map. In the left-hand panels, vertical dotted lines depict the ingress/egress phases of the disk centre (white dwarf). The rotation angle of the spiral arm axis is indicated in each panel (see also text). We adopt the model with an angle $\alpha =46\hbox {$^\circ $ }$ which corresponds to the spirals observed (Baptista et al. 2000; Harlaftis et al. 1999). The model with an angle $\theta _0=136\hbox {$^\circ $ }$ produces an eclipse shape which resembles that observed by Baptista et al. (2002). The two spiral arms of equal brightness are labeled "A'' and "B'' in two of the panels. The dashed lines in the left-hand panels show the contribution of the two spiral arms to the light curves; the dot-dashed lines show the contribution of the symmetric disk component to the light curves; and the solid lines show the total light curve. For visualization purposes, the curve of the symmetric disc component is vertically shifted to match the out-of-eclipse level of the total light curve. Note that the eclipse shape is indeed affected by the rotation of the spiral structure.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=14.2cm]{0643fig3.eps}\end{figure}$ Figure 3: The effect of the phase resolution of the light curve on the image reconstructions. The left-hand panels show data light-curves from the second panel of Fig. 2 for three phase resolutions: $\Delta \phi = 0.005$ , 0.01 and 0.015 cycles. The corresponding asymmetric parts of the eclipse maps for S/N=50 and 25 are presented in logarithmic grayscale.
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm]{0643fig4.eps}\end{figure}$ Figure 4: The effects of accurate phasing of the mid-eclipse (phase offset $\Delta \phi _{0}$ ) on the reconstructions. The value of $\Delta \phi _{0}$ is indicated in each panel; the asymmetric component of the corresponding eclipse maps are shown in the right panels in the same logarithmic greyscale. The notation is similar to that of the other figures.
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In the text

$\begin{figure} \par\includegraphics[width=14.3cm]{0643fig5.eps}\end{figure}$ Figure 5: The effects of dilution of the spiral structure light by a symmetric disk component on the image reconstructions. The left hand panels show model light curves ( $\Delta \phi =0.01$ , S/N=50) for disk models ( $\theta _{0}=46\hbox {$^\circ $ }$ ) in which the spirals contribute 40, 30, 20 and 10 per cent of the total flux. The centre and right hand panels show the asymmetric parts of the corresponding eclipse maps for S/N=50 and 25, respectively. When the emission from the spiral arms suffers large dilution (e.g., fractional contribution of 10%) the method loses its ability to recover the spiral arms and returns only an asymmetric structure with a "crescent'' shape at the outer disk and towards the L₁ point.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=14.2cm]{0643fig6.eps}\end{figure}$ Figure 6: The effect of brightness difference between the two spiral arms on the image reconstructions. The left-hand panels show light curves (S/N=50) for models in which the red and blue arms have equal brightness ( top), and models in which the red arm is fainter than the blue arm in the brightness ratio 1:1.5 ( middle) and 1:2 ( bottom). The right hand panels show the corresponding eclipse maps in log grayscale for three different S/N. Low S/N data (S/N<30) may lead to a loss of the fainter spiral arm. Model arms of equal brightnesses are preserved in the reconstruction map, regardless of the S/N.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm]{0643fig7.eps}\end{figure}$ Figure 7: The light curves, fits, eclipse maps and asymmetric parts of the maps of the blue continuum and of the emission lines He II 4686 Å, Bowen blend, He I 4472 Å and H $\gamma$ (August 1994 outburst; Morales-Rueda et al. 2000). The middle of ingress and egress of the disk centre are marked with vertical dotted lines in the light curves and the fits to the data are also plotted. Note that the eclipse minimum varies in phase between the Balmer and helium emission lines as well as with respect to the continuum minimum. The Roche lobe of the white dwarf is plotted together with the disk radius at 0.6 R_L₁. The donor star lies to the right of the disk map and the ballistic trajectory of the gas is also marked. The reconstruction leads to asymmetric eclipse maps in which a brighter, outer asymmetric arc is seen together with a fainter, inner arc (logarithmic grayscale). The structure resembles that of a two-spiral arm only for the Bowen and He II maps. Doppler tomography resolves clearly the two spiral arms using the out-of-eclipse data (Morales-Rueda et al. 2000).
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In the text

$\begin{figure} \par\includegraphics[width=12.2cm]{0643fig8.eps}\end{figure}$ Figure 8: Velocity-resolved (core/wings) eclipse light curves can reveal with clarity the spiral structure. The core of the H $\gamma$ line profiles ( $\pm 250$ km s^-1) during eclipse result in a reconstructed emission distribution towards the L₁. The wings of the H $\gamma$ line profiles ( $\pm$ 700-1300 km s^-1) during eclipse result in a reconstructed emission distribution consistent with a spiral-arm structure. The earlier mid-eclipse caused by the low-velocity emission component results in the distorted, "crescent''-like eclipse map. Lines, lobes and circles as in Fig. 7. The right-hand panels present S/N ratio maps, made using Monte-Carlo simulations (pixels with $S/N\leq 5$ are painted white).
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=14.2cm]{0643fig3.eps}\end{figure}$	Figure 3: The effect of the phase resolution of the light curve on the image reconstructions. The left-hand panels show data light-curves from the second panel of Fig. 2 for three phase resolutions: $\Delta \phi = 0.005$ , 0.01 and 0.015 cycles. The corresponding asymmetric parts of the eclipse maps for S/N=50 and 25 are presented in logarithmic grayscale.
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$\begin{figure} \par\includegraphics[width=8.3cm]{0643fig4.eps}\end{figure}$	Figure 4: The effects of accurate phasing of the mid-eclipse (phase offset $\Delta \phi _{0}$ ) on the reconstructions. The value of $\Delta \phi _{0}$ is indicated in each panel; the asymmetric component of the corresponding eclipse maps are shown in the right panels in the same logarithmic greyscale. The notation is similar to that of the other figures.
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