All Figures

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9269f01.eps}\end{figure}$ Figure 1: Result of the speckle-observation of T Tauri on February 20, 2000. Shown are modulus ( left) and phase ( right) of the complex visibility (the Fourier-transform of the image). The N-S binary pair causes the fringe pattern in the modulus and the steps in the phase. The fringe pattern due to the binary nature of T Tau S is too weak to be recognizable.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9269f02.eps}\end{figure}$ Figure 2: Image of the T Tau system taken with NACO in the $K_{\rm s}$ photometric band on 2006 Oct. 11, shown with a logarithmic scale.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.4cm,clip]{9269f03.ps}\end{figure}$ Figure 3: The result of the first step in our orbit-fitting procedure. Shown is the minimum $\chi ^2$ for a given period, i.e. we hold the period fixed and search for the optimum set of the remaining 6 orbital elements. Solutions with unphysically high system masses (> $250~M_{\odot}$ ) have been excluded. The ripples at periods $\protect\ga$ 200 years are artefacts caused by the grid search. Note that the $\chi ^2$ shown here has not been divided by the number of degrees of freedom.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.4cm,clip]{9269f04.ps}\end{figure}$ Figure 4: Like Fig. 3, but showing the minimum $\chi ^2$ as a function of eccentricity instead of period. Note that some orbits with e>1 (i.e. unbound orbits) have a $\chi ^2$ not much higher than the minimum.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.3cm,clip]{9269f05.ps}\end{figure}$ Figure 5: Contour plot of the minimum $\chi ^2$ as a function of period and eccentricity. The contour $\chi ^2=151$ marks the 68% confidence intervals for the period or eccentricity (cf. Figs. 3 and 4).
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In the text

$\begin{figure} \par\includegraphics[width=7.1cm,clip]{9269f06.ps}\end{figure}$ Figure 6: Best fitting orbit of T Tau Sb around Sa, in the rest frame of Sa. The observed positions are marked by their error ellipses and lines connecting the observed and calculated position at the time of the observations. The dash-dotted line indicates the line of nodes, the dashed line the periastron, and the arrow shows the direction of the orbital motion. The two dash-dotted ellipses are the measurements by Mayama et al. (2006).
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{9269f07.ps}\end{figure}$ Figure 7: Detailed view of the orbit of T Tau Sb in the rest frame of Sa, and the observations since 2002. The symbols are the same as in Fig. 6.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{9269f08.ps}\end{figure}$ Figure 8: Schematic representation of the stars and orbits in the T Tauri system. The origin of the coordinate system is fixed on T Tau N (marked by a plus sign), therefore the center of mass of Sa and Sb describes an orbit around N. The orbit resulting from our model fits is indicated by the dashed line, while the position of the CM of Sa and Sb on February 20, 2000 is denoted by an asterisk. The orbits of Sa and Sb around their CM according to our model fits are drawn as dotted lines, the positions of the stars on February 20, 2000 (computed from the model) are marked by a diamond and a triangle.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.85cm,clip]{9269f09a.ps}\hsp... ...e*{0.8cm} \includegraphics[angle=90,width=7.85cm,clip]{9269f09d.ps}\end{figure}$ Figure 9: Results of fits for the orbit of the center of mass of T Tau S around T Tau N. The four panels differ in the way observations were treated that did not resolve T Tau S into Sa and Sb. These measurements are marked by crosses, measurements that did resolve T Tau S are marked by asterisks. Note that the crosses show the center of light (which can be observed directly), while the asterisks show the center of mass (which depends on the observations and the model-parameter q). Panel a) shows the result if unresolved observations are not used at all in the fitting procedure. The unresolved measurements are plotted for comparison only. The orbit in panel b) was obtained by adding 25 mas uncertainty to the unresolved observations, while panel c) shows the result if 10 mas are added. For Panel d), the uncertainties given in the literature were used, without any additional errors to compensate for the offset between center of mass and center of light. In all panels, the dotted line shows the path of the center of mass of T Tau S in our models.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{9269f10.ps}\end{figure}$ Figure 10: Minimum $\chi ^2$ as a function of the mass ratio $M_{\rm Sb} / M_{\rm Sa}$ . The dotted line marks $\chi ^2_{\rm min}+1$ , which defines the confidence interval for q.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.7cm,clip]{9269f11.ps}\end{figure}$ Figure 11: Motion of T Tau Sa and Sb in the reference frame of T Tau N. The path of Sa predicted by our orbit models is shown by the dotted line, the path of Sb by the dashed line, and the path of their center of mass (CM) by the dash-dotted line. The predicted positions on January 1, 1997 to 2008 are marked by crosses. The observed positions of Sa are depicted by diamonds, those of Sb by triangles. The solid lines connect the observed and the predicted positions.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9269f01.eps}\end{figure}$	Figure 1: Result of the speckle-observation of T Tauri on February 20, 2000. Shown are modulus ( left) and phase ( right) of the complex visibility (the Fourier-transform of the image). The N-S binary pair causes the fringe pattern in the modulus and the steps in the phase. The fringe pattern due to the binary nature of T Tau S is too weak to be recognizable.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9269f02.eps}\end{figure}$	Figure 2: Image of the T Tau system taken with NACO in the $K_{\rm s}$ photometric band on 2006 Oct. 11, shown with a logarithmic scale.
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$\begin{figure} \par\includegraphics[angle=90,width=7.4cm,clip]{9269f04.ps}\end{figure}$	Figure 4: Like Fig. 3, but showing the minimum $\chi ^2$ as a function of eccentricity instead of period. Note that some orbits with e>1 (i.e. unbound orbits) have a $\chi ^2$ not much higher than the minimum.
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$\begin{figure} \par\includegraphics[angle=90,width=7.3cm,clip]{9269f05.ps}\end{figure}$	Figure 5: Contour plot of the minimum $\chi ^2$ as a function of period and eccentricity. The contour $\chi ^2=151$ marks the 68% confidence intervals for the period or eccentricity (cf. Figs. 3 and 4).
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$\begin{figure} \par\includegraphics[width=7cm,clip]{9269f07.ps}\end{figure}$	Figure 7: Detailed view of the orbit of T Tau Sb in the rest frame of Sa, and the observations since 2002. The symbols are the same as in Fig. 6.
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$\begin{figure} \par\includegraphics[angle=90,width=7.8cm,clip]{9269f10.ps}\end{figure}$	Figure 10: Minimum $\chi ^2$ as a function of the mass ratio $M_{\rm Sb} / M_{\rm Sa}$ . The dotted line marks $\chi ^2_{\rm min}+1$ , which defines the confidence interval for q.
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