All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{7460fg1.eps} \end{figure}$ Figure 1: Ratio between the continuum flux predicted from a theoretical plane-parallel stellar atmosphere with T = 3500 K and values for the logarithm of the gravity ranging between 5.00 and 0.00 and the flux computed from the Engelke function.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{7460fg2.eps} \end{figure}$ Figure 2: Upper panel: model atmosphere spectrum in spherical geometry (black) compared to the theoretical spectrum calculated in plane-parallel geometry (grey) representing the M0 III giant $\beta$ And ( $\lambda$ / $\Delta$ $\lambda$ = 100). Bottom panel: ratio between spherical and plane-parallel spectrum. Stellar parameters are taken from Decin et al. (2003a).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{7460fg3.eps} \end{figure}$ Figure 3: Observed (red - diamonds) versus synthetic (green - stars) magnitude difference between Vega and Sirius (Mag - Mag ) in the Geneva photometric system and the JHKL bands (Verhoelst 2005). Black dotted line represents the difference between both of Kurucz's models used in Cohen et al. (1992a), with stellar parameters T = 9550 K, log g = 3.95, [Fe/H] = -0.3 for Vega and T = 9850 K, log g = 4.25, [Fe/H] = +0.5 for Sirius. However, the Kurucz's model for Sirius is scaled in such a way as to match the observed difference in the Geneva photometric system, yielding an angular diameter for Sirius of 6.15 mas (instead of 6.04 mas as used in Cohen et al. 1992a). Clearly, the (N)IR magnitude differences are not compatible asthey differ by up 10%.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7460fg4.eps} \end{figure}$ Figure 4: UKIRT CGS3 15-22 $\mu$ m spectrum for $\alpha$ Boo (K2 IIIp; unscaled, dash-dot line) and KAO spectrum for $\alpha$ Tau (K5 III; scaled by a factor 1.11, dashed line) are compared with the Engelke approximation (full line) with parameters as used by Cohen et al. (1996b) for $\alpha$ Boo ( T = 4362 K, $\theta_{\rm d}^{}$ = 21.12 mas), and an appropriate theoretical M ARCS model at a resolution $\lambda$ / $\Delta$ $\lambda$ = 1500 (grey line) and at a resolution of $\lambda$ / $\Delta$ $\lambda$ = 70 (dotted line; corresponding to the UKIRT CGS3 resolution), with stellar parameters as determined in Decin et al. (2003a).
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7460fg5.eps} \end{figure}$ Figure 5: Upper panels: Template spectra of $\xi$ Dra (K2 III) and $\alpha$ Tuc (K3 III). The composite spectrum of $\alpha$ Boo (K2 IIIp) has been used to construct the template of $\xi$ Dra (K2 III), and for $\alpha$ Tuc (K3 III) the composite of $\alpha$ Hya (K2 II-III) is used. Lower panels: the total uncertainty attributed to the templated spectra by Cohen et al. (1999). Main absorption features are the CO fundamental around 4.5 $\mu$ m, CO first overtone around 2.3 $\mu$ m, SiO fundamental around 8 $\mu$ m and SiO first overtone around 4.2 $\mu$ m.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7460fg6.eps} \end{figure}$ Figure 6: Upper panel: comparison between the ATLAS, PHOENIX, and M ARCS model spectra. The PHOENIX model is shifted downwards with a factor 10, and the M ARCS model with a factor 100. Middle panel: comparison between the ATLAS, PHOENIX and M ARCS model spectra at a resolution of 100 for $\lambda$ $\le$ 10 $\mu$ m. At longer wavelengths, only the 8 wavelength points as given in the ATLAS models (at 20, 40, 60, 80, 100, 120, 140, and 160 $\mu$ m) are retained. Difference between PHOENIX and M ARCS model fluxes is barely visible. Bottom panel: ratio between MARCS and ATLAS (black) and PHOENIX (gray) model fluxes.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{7460fg7.eps} \end{figure}$ Figure 7: Contribution of CO (blue), SiO (orange), OH (green), CN (pink), H₂O (red), atoms (purple) to the 2-200 $\mu$ m synthetic spectrum calculated from the atmosphere model with stellar parameters T = 4320 K, log g [cm/s²] = 1.50, mass M = 1.1 M, [Fe/H] = -0.50, microturbulence $\xi_{t}^{}$ = 2 km s^-1, $\varepsilon$ (C) = 7.96, $\varepsilon$ (N) = 7.61, $\varepsilon$ (O) = 8.68, $\varepsilon$ (Mg) = 7.33, $\varepsilon$ (Si) = 7.20, and ¹²C/¹³C = 7. The first six panels display the contribution at a resolution $\Delta$ $\lambda$ = 0.5 Å in color and at a medium resolution $\lambda$ / $\Delta$ $\lambda$ = 1500 in black. The total contribution to the full spectrum is shown in the seventh panel at the high resolution of $\Delta$ $\lambda$ = 0.5 Å, and in the bottom panel at the medium resolution of $\lambda$ / $\Delta$ $\lambda$ = 1500. Note the lack of atomic absorption features for wavelengths longer than $\sim$ 50 $\mu$ m.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7460fg8.eps}\end{figure}$ Figure 8: Ratio between synthetic spectra with differing stellar parameters at a resolution of $\lambda$ / $\Delta$ $\lambda$ = 100. The standard model has the same stellar parameters as in Fig. 7. Upper panel: ratio between a synthetic spectrum with T = 4320 K and with T = 4520 K. Middle panel: ratio between log g = 1.50 and log g = 1.70. Bottom panel: ratio between [Fe/H] = -0.50 and [Fe/H] = -0.30.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7460fg9.eps}\end{figure}$ Figure 9: Ratio between the synthetic spectrum calculated with the H ^- absorption coefficients of Bell & Berrington (1987) and the spectrum based on the H ^- absorption coefficients of Stilley & Callaway (1970). The same stellar parameters as in Fig. 7 are used, data are reduced to a resolution of $\lambda$ / $\Delta$ $\lambda$ = 100.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{7460fg10.eps} \end{figure}$ Figure 10: Comparison between the various reference SEDs discussed in this paper in the 2 to 200 $\mu$ m wavelength range. $\alpha$ Boo (K2 IIIp) and $\beta$ And (M0 III) represent two composites from the CWW network, and $\xi$ Dra (K2 III) and $\alpha$ Tuc (K3 III) represent two templates. M ARCS model atmosphere spectra are displayed at a resolution $\lambda$ / $\Delta$ $\lambda$ = 100. IRAS LRS and PSC data and several photometric data points collected from the ISO GBPP are also shown.
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In the text

$\begin{figure} \par\includegraphics[width=9cm,clip]{7460fg11.eps}\end{figure}$ Figure 11: Upper panel: comparison between the M ARCS model spectrum of $\alpha$ Boo ( $\lambda$ / $\Delta$ $\lambda$ = 100) and predictions using the Engelke function with parameters T = 4362 K and $\theta_{\rm d}^{}$ = 21.12 mas (dashed line), and T = 4320 K and $\theta_{\rm d}^{}$ = 20.72 mas (dotted line). Bottom panel: ratio between M ARCS model predictions and both Engelke functions.
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In the text

$\begin{figure} \par\includegraphics[width=9cm,clip]{7460fg12.eps}\end{figure}$ Figure 12: Upper panel: comparison between the M ARCS model spectrum of $\alpha$ Boo and $\xi$ Dra at a resolution of 1500. Both spectra have a fictitious angular diameter of 1 mas. Bottom panel: same as for the upper panel, but now at a resolution of 100. In regions of strong molecular absorption, the maximum difference is 15% for $\lambda$ / $\Delta$ $\lambda$ = 1500, and 8% for $\lambda$ / $\Delta$ $\lambda$ = 100.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{7460fg1.eps} \end{figure}$	Figure 1: Ratio between the continuum flux predicted from a theoretical plane-parallel stellar atmosphere with T = 3500 K and values for the logarithm of the gravity ranging between 5.00 and 0.00 and the flux computed from the Engelke function.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{7460fg2.eps} \end{figure}$	Figure 2: Upper panel: model atmosphere spectrum in spherical geometry (black) compared to the theoretical spectrum calculated in plane-parallel geometry (grey) representing the M0 III giant $\beta$ And ( $\lambda$ / $\Delta$ $\lambda$ = 100). Bottom panel: ratio between spherical and plane-parallel spectrum. Stellar parameters are taken from Decin et al. (2003a).
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7460fg9.eps}\end{figure}$	Figure 9: Ratio between the synthetic spectrum calculated with the H ^- absorption coefficients of Bell & Berrington (1987) and the spectrum based on the H ^- absorption coefficients of Stilley & Callaway (1970). The same stellar parameters as in Fig. 7 are used, data are reduced to a resolution of $\lambda$ / $\Delta$ $\lambda$ = 100.
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