All Figures

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{H4248F1.eps}} \end{figure}$ Figure 1: Composite of three narrow-band images of the central region of NGC 2024 obtained with NTT/SOFI (blue: P $\beta$ ; red: Br $\gamma$ ; green: H₂). North is up and East to the left; the image size is $5' \times 5'$ (at the distance of NGC2024 this corresponds to $0.5 \times 0.5$ pc). The upper left panel zooms in on the region around IRS2: about 5'' to the north-west we find IRS2b, the ionizing star of NGC 2024. Also some previously proposed candidate ionizing stars are indicated. The vertical stripes are instrumental artifacts caused by the brightest stars.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{H4248F2.eps}} \end{figure}$ Figure 2: Color-magnitude diagram of the brightest stars in the central region of NGC 2024. The vertical (dotted) lines indicate the position of the main sequence for different amounts of visual extinction (A_V). The magnitudes are obtained through narrow-band observations. The diagonal (dashed) line is the dereddening line of IRS2b, demonstrating that IRS2b is the intrinsically brightest star of the embedded population. IRS2 (saturated in K) probably is a B star with a strong infrared excess due to a circumstellar disk (Lenorzer et al. 2003). The dashed-dotted line is the detection limit in (J-K) following from the detection limits in J and K.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{H4248F3.eps}} \end{figure}$ Figure 3: K-band spectrum of IRS2b, obtained with VLT/ISAAC, showing He I 2.1127, 2.1138 $\mu$ m and Br $\gamma$ 2.166 $\mu$ m in absorption.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{H4248F4.eps} \end{figure}$ Figure 4: Left: the upper part of the theoretical HRD. The shaded region indicates the position of IRS2b for which all observational constraints on L and $T_{\rm eff}$ are fulfilled. The diagonal area represents the constraint provided by the observed K-band magnitude. The K-band spectrum implies that $T_{\rm eff} \leq 34~000$ K. Also shown are the theoretical evolutionary tracks and isochrones from Lejeune & Schaerer (2001). Right: the same region of the HRD as shown in the left panel, but now including the regions in the HRD capable to produce Q₀ and Q₁ for comparison.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{H4248F3.eps}} \end{figure}$	Figure 3: K-band spectrum of IRS2b, obtained with VLT/ISAAC, showing He I 2.1127, 2.1138 $\mu$ m and Br $\gamma$ 2.166 $\mu$ m in absorption.
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