All Figures

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{8381fig1.eps} \end{figure}$ Figure 1: NACO Ks-band image of the low-mass binary Cha H $\alpha$ 2 from 25 March 2005. The southwestern component appears slightly brighter, hence we call this component A (or SW), the fainter northeastern component B (or NE).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8381fig2.eps} \end{figure}$ Figure 2: Observed separation between the two components of Cha H $\alpha$ 2. The archival data point from 2005 and our two measurements from 2006 and 2007 are shown. The short-dashed lines enclose the area for constant separation. The dash-dotted line is the change expected if the B component is a non-moving background star. The opening cone enclosed by the solid lines are its estimated errors. The waves of this cone show the differential parallactic motion, which has to be taken into account if the other component is a non-moving background star. The opening long-dashed cone indicates the amplitude of possible orbital motion.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{8381fig3.eps} \end{figure}$ Figure 3: Observed position angle between the two components of Cha H $\alpha$ 2 (measured from the brighter component north over east to south). See Fig. 2 for details.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8381fig4.eps} \end{figure}$ Figure 4: Observed separation between the two components of Cha H $\alpha$ 2. Same as Fig. 2, but the opening cone enclosed by the solid lines is the change expected if the A component is a non-moving background star.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8381fig5.eps} \end{figure}$ Figure 5: Same as Fig. 3, but position angle between the two components measured from the B component and assuming the A component is a non-moving background star.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=16.6cm,clip]{8381fig6.eps} \end{figure}$ Figure 6: Bottom: spectrum of both components from the optical part to the near-infrared combined from data from Comerón et al. (2000) and data from the ESO Paranal and La Silla instruments ISAAC and SofI retrieved from the ESO Science Archive Facility. Top: the best fit to the spectrum: GAIA models computed with the PHOENIX code by Brott & Hauschildt (2005) for a temperature of 3000 K, $\log{g}$ of 4.0 and a visual extinction $A_{\rm V}\simeq 4.3$ mag. Note that the missing flux depression in J-band (between 1.2 and 1.3 micron) as well as in the peak of the H-band (around 1.65 micron) is due to missing FeH opacities in the spectral models. Note the strong H $\alpha$ emission in Cha H $\alpha$ 2 at 0.6568 $\mu$ m.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{8381fig7.eps} \end{figure}$ Figure 7: Plot of the true and expected position of Cha H $\alpha$ 2 A if Cha H $\alpha$ 2 B is a non-moving background star. Shown are the NACO measurements from 2005 to 2007, as in Figs. 2-5, and, in addition, the measurement from 2000 using the Hubble Space Telescope in R-band by Neuhäuser et al. (2002). As in Fig. 2, the line showing parallactic wobbles is the expected position of component A if component B is a non-moving background star, in this case from epoch 2000.8 until 2007.2, from left to right. The opening dashed cone are its errors. The HST data point obtained at epoch 2000.8 is significantly different (2.3 $\sigma$ ) from the expectation, if background.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{8381fig8.eps} \end{figure}$ Figure 8: Observed K-band NACO spectra of the Cha H $\alpha$ 2 system. In each panel, one of the components of the system is shown ( top in each panel) compared to the higher S/N spectrum of both objects combined from Fig. 6 ( bottom in each panel). Top: component A (southwestern component). Bottom: component B (northeastern component). Both spectra are dereddened using the visual extinction of $A_{\rm V}\simeq 4.3$ mag derived from the spectra shown in Fig. 6.
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In the text

Color version

$\begin{figure} \par\includegraphics[angle=90,width=16.6cm,clip]{8381Onl6.eps} \end{figure}$ Figure 6: Spectrum of both components from the optical part to the near-infrared combined from data from Comerón et al. (2000) (purple), and data from the ESO Paranal and La Silla instruments ISAAC (blue) and SofI (black: blue arm spectra, red: red arm spectra) retrieved from the ESO Science Archive Facility. The best fit to the spectrum, a GAIA model computed with the PHOENIX code by Brott & Hauschildt (2005) for a temperature of 3000 K, $\log~g$ of 4.0 and a visual extinction of 4.3 mag is superimposed in green. Note that the missing flux depression in J-band (between 1.2 and 1.3 micron) as well as in the peak of the H-band (around 1.65 micron) is due to missing FeH opacities in the spectral models. Note the strong H $\alpha$ emission in Cha H $\alpha$ 2 at 0.6568 $\mu$ m.
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{8381fig1.eps} \end{figure}$	Figure 1: NACO Ks-band image of the low-mass binary Cha H $\alpha$ 2 from 25 March 2005. The southwestern component appears slightly brighter, hence we call this component A (or SW), the fainter northeastern component B (or NE).
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{8381fig3.eps} \end{figure}$	Figure 3: Observed position angle between the two components of Cha H $\alpha$ 2 (measured from the brighter component north over east to south). See Fig. 2 for details.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{8381fig4.eps} \end{figure}$	Figure 4: Observed separation between the two components of Cha H $\alpha$ 2. Same as Fig. 2, but the opening cone enclosed by the solid lines is the change expected if the A component is a non-moving background star.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{8381fig5.eps} \end{figure}$	Figure 5: Same as Fig. 3, but position angle between the two components measured from the B component and assuming the A component is a non-moving background star.
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