All Figures

$\begin{figure} \par\includegraphics[width=13cm,clip]{2136fig1.ps} \end{figure}$ Figure 1: Green and red spectrum of WR 20a. The top panel corresponds to the spectrum observed at phase 0.895 (HJD 2 453 179.472), whilst the lower panel corresponds to phase 0.798 (HJD 2 453 042.734). In addition to the telluric absorptions, the bulk of the absorption features in these spectral domains are due to diffuse interstellar bands (the identifications are taken from Herbig 1995). The stellar spectrum is dominated by strong emission lines of H $\alpha$ and several blends due to N IV lines. Note also the absence of He I $\lambda$ 5879 and the presence of C IV $\lambda \lambda$ 5801, 5812 in emission.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{2136fig2.ps} \end{figure}$ Figure 2: Line profile variability of the H $\alpha$ ( left) and He II $\lambda$ 4686 ( right) emission lines in the spectrum of WR 20a. The normalized spectra are vertically shifted by 0.7. The orbital phases of the observations, computed using the ephemeris of Bonanos et al. (2004), are given on the right of each panel. Note the striking similarity between the profiles of the two lines at similar orbital phases.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2136fig3.ps} \end{figure}$ Figure 3: Upper panel: variations of the measured EW of the H $\alpha$ emission line between 6499 and 6646 Å (open symbols) and of the EWs corrected for the variations of the continuum (asterisks). The open square and the cross correspond respectively to the measured and the corrected EW of the line in the June 2004 spectrum. Middle panel: variations of the measured EW of the He II $\lambda$ 4686 line between 4656 and 4723 Å (see text). The triangle refers to the measurement from our 2002 campaign (see text). Lower panel: photometric light curve of WR 20a in the I-band as reported by Bonanos et al. (2004).
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In the text

$\begin{figure} \par\includegraphics[width=7.9cm,clip]{2136fig4.ps} \end{figure}$ Figure 4: Doppler map of the H $\alpha$ emission line in the spectrum of WR 20a. The crosses correspond to the radial velocity amplitudes of the centre of mass of the primary ( bottom) and secondary ( top) as derived from our orbital solution in Paper I. The shape of the Roche lobe in velocity-space (thick dashed line) has been calculated for a mass ratio of 0.99. The Doppler map was computed with v_z set to -50 km s^-1. The black dot indicates the position of the highest peak and the contours correspond to levels of 0.95, 0.80, 0.65, 0.50, 0.35 and 0.20 times the maximum emissivity. The insert in the lower right corner illustrates the Doppler map of a constant Gaussian with a FWHM corresponding to the spectral resolution of our data and observed with the same sampling as the actual data. This figure appears in colour in the electronic version of the journal.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{2136fig5.ps} \end{figure}$ Figure 5: Same as Fig. 4, but for the He II $\lambda$ 4686 emission.
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In the text

$\begin{figure} \par\includegraphics[width=11.4cm,clip]{2136fig6.ps} \end{figure}$ Figure 6: Comparison between the observed spectrum at phase $\sim$ 0.46 (solid line) and the predictions from our best atmospheric model (dashed line).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2136fig7.ps} \end{figure}$ Figure 7: Schematic view of a possible wind interaction process in WR 20a. The direction of the line of sight is projected on the orbital plane for the phases of quadrature and conjunction. The peaks of the H $\alpha$ and He II $\lambda$ 4686 emissions arise in the shaded area, though the full emitting region could extend beyond the limits of our figure.
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In the text

$\begin{figure} \par\includegraphics[width=6.7cm,clip]{2136fig8.ps} \end{figure}$ Figure 8: ROSAT-HRI X-ray contours overlaid on a DSS image of the Westerlund 2 cluster. The X-ray emission associated with WR 20a (10h23min58s, $-57^{\circ }$ 45 $^\prime$ 49 $^{\prime \prime }$ , J2000; indicated by the arrow) is clearly seen. The bright X-ray source to the north of the cluster core appears to be most likely associated with star No. 18 (O7:V) of Moffat et al. (1991).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2136fig9.ps} \end{figure}$ Figure 9: Position of the components of WR 20a in the Hertzsprung-Russell diagram. The evolutionary tracks for single stars of initial mass 40, 60 and 85 $M_{\odot }$ as well as the isochrones corresponding to ages of 1, 2 and 3 Myr are from Schaller et al. (1992) for metallicity $Z = Z_{\odot }$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{2136fig5.ps} \end{figure}$	Figure 5: Same as Fig. 4, but for the He II $\lambda$ 4686 emission.
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$\begin{figure} \par\includegraphics[width=11.4cm,clip]{2136fig6.ps} \end{figure}$	Figure 6: Comparison between the observed spectrum at phase $\sim$ 0.46 (solid line) and the predictions from our best atmospheric model (dashed line).
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$\begin{figure} \par\includegraphics[width=8cm,clip]{2136fig7.ps} \end{figure}$	Figure 7: Schematic view of a possible wind interaction process in WR 20a. The direction of the line of sight is projected on the orbital plane for the phases of quadrature and conjunction. The peaks of the H $\alpha$ and He II $\lambda$ 4686 emissions arise in the shaded area, though the full emitting region could extend beyond the limits of our figure.
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$\begin{figure} \par\includegraphics[width=6.7cm,clip]{2136fig8.ps} \end{figure}$	Figure 8: ROSAT-HRI X-ray contours overlaid on a DSS image of the Westerlund 2 cluster. The X-ray emission associated with WR 20a (10h23min58s, $-57^{\circ }$ 45 $^\prime$ 49 $^{\prime \prime }$ , J2000; indicated by the arrow) is clearly seen. The bright X-ray source to the north of the cluster core appears to be most likely associated with star No. 18 (O7:V) of Moffat et al. (1991).
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2136fig9.ps} \end{figure}$	Figure 9: Position of the components of WR 20a in the Hertzsprung-Russell diagram. The evolutionary tracks for single stars of initial mass 40, 60 and 85 $M_{\odot }$ as well as the isochrones corresponding to ages of 1, 2 and 3 Myr are from Schaller et al. (1992) for metallicity $Z = Z_{\odot }$ .
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