All Figures

$\begin{figure} \par\includegraphics[angle=90,width=8.2cm,clip]{0136fg03.eps} \end{figure}$ Figure 3: Observed SED vs. SED constructed with the best-fit parameters. The observed SED is here supposed to be representative of the whole cluster, even though the slits (in particular the optical one) only sample a portion of the cluster.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{0136fg04.eps} \end{figure}$ Figure 4: Evolution of $W({\rm H}\beta )$ (top), ${\mathcal N}({\rm WN})$ (middle) and ${\mathcal N}({\rm BSG})$ (bottom) with the cluster age, for Z=0.004, $m_{\rm up}=120$ $M_{\odot }$ and the IMF slopes $\alpha =2.3$ 5 (full lines), 1 (short-dashed lines) and 3.3 (dotted lines). In the $W({\rm H}\beta )$ panel, the full horizontal line shows the observed value, and the long-dashed one, the 3 $\sigma$ limit. In the ${\mathcal N}({\rm WN})$ panel, the horizontal line and the arrow are here to remind that at least one WN star is present in the cluster.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{0136fg05.eps} \end{figure}$ Figure 5: Same as Fig. 4 for Z=0.008.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=4cm,clip]{0136fg06.eps}\hspac... ...pace*{2mm} \includegraphics[angle=90,width=4cm,clip]{0136fg09.eps} \end{figure}$ Figure 6: Observed vs. synthetic UV spectra for different IMF slopes. The synthetic spectra were convolved by a 5 Å FWHM Gaussian curve to match IUE's resolution.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=4cm,clip]{0136fg10.eps}\hspac... ...space*{2mm} \includegraphics[angle=90,width=4cm,clip]{0136fg13.eps} \end{figure}$ Figure 7: STIS vs. LMC/SMC spectra: B0II, B0I, WNL and WCL, respectively. The 1600-1700 Å region was unavailable for the B0I star.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{0136fg14.eps} \end{figure}$ Figure 8: Optical spectra near the WR He II $\lambda$ 4686 bump, extracted from the blue CAHA spectrum around stars #1 and #2 of Table 4.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.5cm,clip]{0136fg23.eps} \end{figure}$ Figure 11: Histogram of the dispersion of the stellar color excesses E_B-Varound the nebular one 0.11. The abscissa axis variable is the discrepancy term $\chi =(E_{B-V}-0.11)/\sigma (E_{B-V})$ , where $\sigma (E_{B-V})$ is the uncertainty of the considered measurement of E_B-V. The histogram includes the 173 stars observed simultaneously through filters F547W and F439W. The overplotted curve is the theoretical expected distribution in the case of a unique real value E_B-V=0.11 and of well-determined measurement uncertainties.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{0136fg30.eps} \end{figure}$ Figure 14: Final adopted (M₄₃₉,M₁₇₀-M₅₄₇) diagram.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{0136fg31.eps} \end{figure}$ Figure 15: Final adopted HR diagram for all the detected stars. The circles show the selected individual stellar model. The dashed part of the diagram is the WR branch. The two dotted curves represent the HR diagram at 3.0 Myr (upper curve) and 5.5 Myr (lower curve).
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.2cm,clip]{0136fg32.eps} \end{figure}$ Figure 16: Optical and UV SEDs synthesized for Z=0.008 and $\tau =4.2$ Myr with the individual stellar models. For better visibility and comparison with Fig. 3, the luminosities of the observed optical and UV parts were rescaled with multiplicative factors, in order to fit the integrated luminosities in band F439W and F170W, respectively. The synthetic spectra were normalized using the same factors.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{0136fg33.eps} \end{figure}$ Figure 17: UV spectrum synthesized for Z=0.008 and $\tau =4.2$ Myr with the individual stellar models.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{0136fg34.eps} \end{figure}$ Figure 18: IMF histogram and fit. Full line: best fit. Dashed line: fit for the Salpeter slope. The error bars are equivalent to 1 $\sigma$ Gaussian ones, in terms of likelihood, and must be interpreted this way: for a model that goes through the extremity of an error bar, the observed value whose error bar is being considered has a likelihood to occur of $\exp(-1/2)$ times the maximum likelihood of the model at this abscissa.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.4cm,clip]{0136fg35.eps}\par... ...pace*{2mm}\includegraphics[angle=90,width=8.2cm,clip]{0136fg36.eps} \end{figure}$ Figure 19: Top: SEDs of the whole cluster (full line), of the 6 brightest stars (dashed line) and of the remaining 167 stars (dotted line). Bottom: ratio of the brightest 6 stars SED (full line) and of the remaining 167 star SED (dotted line) to the total SED.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{0136fg37.eps} \end{figure}$ Figure 20: $(\log Q({\rm H}^0),M_{439})$ diagram of the detected stars along the the theoretical isochrone. The WR branch is the dashed part of the curve.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.6cm,clip]{0136fg38.eps} \end{figure}$ Figure 21: Star-by-star constructed SED (full lines), and SEDs of the analytical populations, for Z=0.008 and $m_{\rm up}=120$ $M_{\odot }$ , at 2.8 Myr (dashed line) and 4.2 Myr (dotted line).
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.6cm,clip]{0136fg39.eps} \end{figure}$ Figure 22: Histogram of $\log W({\rm H}\beta)$ resulting from the 10⁶ Monte-Carlo discrete IMF realizations.
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{0136fg01.eps} \end{figure}$ Figure 1: HST image of NGC 588 in filter F439W and the spectral slits. The peculiar stars (WNL, WN) are discussed in Sect. 6.
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{0136fg02.eps} \end{figure}$ Figure 2: H $\alpha$ +[N II] image of NGC 588 and CAHA and IUE slits. The contours represent the H $\alpha$ continuum.
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In the text

$\begin{figure} \par\includegraphics[width=4.1cm,clip]{0136fg15.eps}\hspace*{2mm}... ...17.eps}\hspace*{3mm} \includegraphics[width=4cm,clip]{0136fg18.eps} \end{figure}$ Figure 9: Illustration of the dereddening procedure. The isochrone shown here was established for an age of 3.5 Myr and for Z=0.008. Panel a): observed (M₄₃₉,M₃₃₆-M₅₄₇) diagram. Other panels: (M₄₃₉,M₁₇₀-M₅₄₇) diagram dereddened with the (M₄₃₉,M₃₃₆-M₅₄₇) one and the Galactic b), LMC c) and SMC d) laws. The dotted lines are the WR branches of the isochrone curves. The two WR stars are signalized by open circles. The arrows indicate the shift that the observational points undergo by if dereddened for E_B-V=0.1. In the diagrams of panels b), c) and d), the error bars account for uncertainties of E_B-V.
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In the text

$\begin{figure} \par\includegraphics[width=4.1cm,clip]{0136fg19.eps}\hspace*{2mm}... ....eps}\hspace*{3.2mm} \includegraphics[width=4cm,clip]{0136fg22.eps} \end{figure}$ Figure 10: Same as Fig. 9 for the isochrone of 4.5 Myr.
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In the text

$\begin{figure} \par\includegraphics[width=4cm,clip]{0136fg24.eps}\hspace*{2mm} \includegraphics[width=4cm,clip]{0136fg25.eps} \end{figure}$ Figure 12: Observed vs. isochrone (M₄₃₉,M₁₇₀-M₅₄₇) diagram for Z=0.004. The two WR stars are marked with open circles. The WR branches of the isochrones are shown as dashed lines.
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In the text

$\begin{figure} \par\includegraphics[width=4.2cm,clip]{0136fg26.eps}\hspace*{2mm}... ....eps}\hspace*{2mm} \includegraphics[width=4.2cm,clip]{0136fg29.eps} \end{figure}$ Figure 13: Same as Fig. 12 for Z=0.008.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8.2cm,clip]{0136fg03.eps} \end{figure}$	Figure 3: Observed SED vs. SED constructed with the best-fit parameters. The observed SED is here supposed to be representative of the whole cluster, even though the slits (in particular the optical one) only sample a portion of the cluster.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{0136fg05.eps} \end{figure}$	Figure 5: Same as Fig. 4 for Z=0.008.
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$\begin{figure} \par\includegraphics[angle=90,width=4cm,clip]{0136fg06.eps}\hspac... ...pace*{2mm} \includegraphics[angle=90,width=4cm,clip]{0136fg09.eps} \end{figure}$	Figure 6: Observed vs. synthetic UV spectra for different IMF slopes. The synthetic spectra were convolved by a 5 Å FWHM Gaussian curve to match IUE's resolution.
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$\begin{figure} \par\includegraphics[angle=90,width=4cm,clip]{0136fg10.eps}\hspac... ...space*{2mm} \includegraphics[angle=90,width=4cm,clip]{0136fg13.eps} \end{figure}$	Figure 7: STIS vs. LMC/SMC spectra: B0II, B0I, WNL and WCL, respectively. The 1600-1700 Å region was unavailable for the B0I star.
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$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{0136fg14.eps} \end{figure}$	Figure 8: Optical spectra near the WR He II $\lambda$ 4686 bump, extracted from the blue CAHA spectrum around stars #1 and #2 of Table 4.
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{0136fg30.eps} \end{figure}$	Figure 14: Final adopted (M₄₃₉,M₁₇₀-M₅₄₇) diagram.
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$\begin{figure} \par\includegraphics[width=7.5cm,clip]{0136fg31.eps} \end{figure}$	Figure 15: Final adopted HR diagram for all the detected stars. The circles show the selected individual stellar model. The dashed part of the diagram is the WR branch. The two dotted curves represent the HR diagram at 3.0 Myr (upper curve) and 5.5 Myr (lower curve).
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$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{0136fg33.eps} \end{figure}$	Figure 17: UV spectrum synthesized for Z=0.008 and $\tau =4.2$ Myr with the individual stellar models.
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$\begin{figure} \par\includegraphics[angle=90,width=8.4cm,clip]{0136fg35.eps}\par... ...pace*{2mm}\includegraphics[angle=90,width=8.2cm,clip]{0136fg36.eps} \end{figure}$	Figure 19: Top: SEDs of the whole cluster (full line), of the 6 brightest stars (dashed line) and of the remaining 167 stars (dotted line). Bottom: ratio of the brightest 6 stars SED (full line) and of the remaining 167 star SED (dotted line) to the total SED.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{0136fg37.eps} \end{figure}$	Figure 20: $(\log Q({\rm H}^0),M_{439})$ diagram of the detected stars along the the theoretical isochrone. The WR branch is the dashed part of the curve.
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$\begin{figure} \par\includegraphics[angle=90,width=8.6cm,clip]{0136fg38.eps} \end{figure}$	Figure 21: Star-by-star constructed SED (full lines), and SEDs of the analytical populations, for Z=0.008 and $m_{\rm up}=120$ $M_{\odot }$ , at 2.8 Myr (dashed line) and 4.2 Myr (dotted line).
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$\begin{figure} \par\includegraphics[angle=90,width=8.6cm,clip]{0136fg39.eps} \end{figure}$	Figure 22: Histogram of $\log W({\rm H}\beta)$ resulting from the 10⁶ Monte-Carlo discrete IMF realizations.
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$\begin{figure} \par\includegraphics[width=7.7cm,clip]{0136fg01.eps} \end{figure}$	Figure 1: HST image of NGC 588 in filter F439W and the spectral slits. The peculiar stars (WNL, WN) are discussed in Sect. 6.
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$\begin{figure} \par\includegraphics[width=7.7cm,clip]{0136fg02.eps} \end{figure}$	Figure 2: H $\alpha$ +[N II] image of NGC 588 and CAHA and IUE slits. The contours represent the H $\alpha$ continuum.
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$\begin{figure} \par\includegraphics[width=4.1cm,clip]{0136fg19.eps}\hspace{2mm}... ....eps}\hspace{3.2mm} \includegraphics[width=4cm,clip]{0136fg22.eps} \end{figure}$	Figure 10: Same as Fig. 9 for the isochrone of 4.5 Myr.
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$\begin{figure} \par\includegraphics[width=4cm,clip]{0136fg24.eps}\hspace*{2mm} \includegraphics[width=4cm,clip]{0136fg25.eps} \end{figure}$	Figure 12: Observed vs. isochrone (M₄₃₉,M₁₇₀-M₅₄₇) diagram for Z=0.004. The two WR stars are marked with open circles. The WR branches of the isochrones are shown as dashed lines.
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$\begin{figure} \par\includegraphics[width=4.2cm,clip]{0136fg26.eps}\hspace{2mm}... ....eps}\hspace{2mm} \includegraphics[width=4.2cm,clip]{0136fg29.eps} \end{figure}$	Figure 13: Same as Fig. 12 for Z=0.008.
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