All Figures

$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{2685fig1.ps} \end{figure}$ Figure 1: Plot of mean correlation coefficient of the maser spots (dashed curve; see text) and mean direction of the normalised proper motions (solid curve) versus source distance. The vertical dotted and solid lines mark respectively d=1.4 and 1.7 kpc. The grey area denotes the range of possible jet position angles.
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In the text

$\begin{figure} \par\includegraphics[angle=0,width=15cm,clip]{2685fig2.ps} \end{figure}$ Figure 2: a) Map of the H₂O maser spots detected towards IRAS 20126+4104 by us (small circles), MCR (squares), and EFCE (triangles) overlayed on a contour map of the 3.6 cm continuum emission (Hofner et al. 1999). Also shown are the OH maser emission peaks observed by EFCE (big circles). The errors on the absolute positions of the H₂O maser spots detected by us are given in Table 1, while those of MCR and EFCE are respectively 30 mas and 15 mas; for the OH masers the error is 25 mas. The colour denotes the LSR velocity of each spot according to the colour scale in the bottom panel. The solid lines indicate the conical jet which represents the best fit to the H₂O maser spots obtained with the model discussed in Sect. 4. b) Enlargement of the central region illustrating the locations and absolute proper motions (corrected for parallax, solar motion with respect to the LSR, and galactic rotation) of the H₂O maser spots detected in this study. Offsets in RA and Dec are measured with respect to RA(J2000 $)=20^{\rm h}$ 14 $^{\rm m}$ 26 $.\!\!^{\rm s}$ 0253, Dec(J2000)=41 $^\circ$ 13 $^\prime$ 32 $.\!\!^{\prime\prime}$ 666. No proper motion measurement is available for points without an associated arrow. The colour coding is the same as for the top panel. Note that the systemic LSR velocity of IRAS 20126+4104 is -3.5 km s^-1.
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In the text

$\begin{figure} \par\includegraphics[angle=0,width=8.5cm,clip]{2685fig3.ps} \end{figure}$ Figure 3: Plot of speed versus separation (measured on the plane of the sky) from the 3.6 cm continuum peak for all H₂O maser spots of Fig. 2b with measured proper motions (filled circles). Also shown is a plot of the l.o.s. component of the velocity for all spots detected in this study (empty circles). Note the tendency of the speed to increase with distance from the YSO.
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In the text

$\begin{figure} \par\includegraphics[angle=0,width=8.5cm,clip]{2685fig4.ps} % \end{figure}$ Figure 4: Comparison between the observed velocities (filled circles) and those obtained from our model fit (empty circles). The top and middle panel show respectively the proper motions in the RA and Dec directions, while the bottom panel plots the LSR velocity. Note that data points missing in the top and middle panels correspond to spots without measured proper motions. The dashed line marks the systemic velocity (-3.5 km s^-1) of IRAS 20126+4104. The number on the x-axis indicates the maser spot according to the notation in Table 1.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=14cm,clip]{2685fig5.ps} \end{figure}$ Figure 5: Variability plot of the H₂O maser emission in IRAS 20126+4104. The grey scale map represents the intensity measured with the Medicina antenna as a function of time and LSR velocity. The value t=0 corresponds to September 12, 1995. The white squares mark the positions of the the peak velocities of the lines detected in the Medicina spectra, while the error bars correspond to the line full width at half maximum ( FWHM). Both the peak velocity and line width have been obtained with a Gaussian fit. The black squares indicate the peak velocities of the spots observed in the VLBA, VLBI, and MERLIN observations of MCR, this study, and EFCE respectively. Only the first and third VLBI epochs are shown here to preserve readability of the figure. The horizontal solid line marks the systemic velocity (-3.5 km s^-1) of IRAS 20126+4104. The dashed lines outline the linear variation of velocity versus time observed in three spectral features, labeled with numbers (1) to (3).
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{2685fig6.ps} \end{figure}$ Figure 6: Map of the H₂O maser spots belonging to feature (2) in Fig. 5. The (0,0) position corresponds to RA(J2000 $)=20^{\rm h}$ 14 $^{\rm m}$ 26 $.\!\!^{\rm s}$ 0253, Dec(J2000)=41 $^\circ$ 13 $^\prime$ 32 $.\!\!^{\prime\prime}$ 666. Black circles indicate our measurements, squares those by MCR, and triangles those by EFCE. The error bars indicate the 1 $\sigma$ uncertainty in the astrometry of the MCR and EFCE measurements (the error on our data is less than the size of the symbols). Note that the error in the relative positions of the spots in each data set is of order 1 mas. The arrows denote the proper motions measured by us, while the empty circles mark the positions of the same spots extrapolated to the dates of MCR (November 21, 1997) and EFCE's (March 2002) observations, on the basis of the current spot position, proper motion, and acceleration (see text).
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{2685fig7.ps} \end{figure}$ Figure 7: Map of the H₂O maser spots belonging to feature (1) in Fig. 5. The (0,0) position corresponds to RA(J2000 $)=20^{\rm h}$ 14 $^{\rm m}$ 26 $.\!\!^{\rm s}$ 0253, Dec(J2000)=41 $^\circ$ 13 $^\prime$ 32 $.\!\!^{\prime\prime}$ 666. Squares indicate measurements by MCR and triangles those by EFCE. The error bars indicate the 1 $\sigma$ uncertainty on the astrometry. The error on the relative position of the spots in each data set is of order 1 mas. The starred polygon marks the position of the YSO according to our conical model fit, while the solid lines denote the projection of the cone on the plane of the sky.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{2685fig8.ps} \end{figure}$ Figure 8: Peak velocity of feature (1) and (2) (see Fig. 5) as a function of time. Error bars denote line FWHMs. The dashed lines are the same as in Fig. 5 and represent linear fits to the data, while dotted and solid lines are fits of the type $V\propto (t-t_0)^{-1/2}$ and $V\propto \exp[-(t-t_0)/\tau]$ , respectively.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{2685fig1.ps} \end{figure}$	Figure 1: Plot of mean correlation coefficient of the maser spots (dashed curve; see text) and mean direction of the normalised proper motions (solid curve) versus source distance. The vertical dotted and solid lines mark respectively d=1.4 and 1.7 kpc. The grey area denotes the range of possible jet position angles.
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$\begin{figure} \par\includegraphics[angle=0,width=8.5cm,clip]{2685fig3.ps} \end{figure}$	Figure 3: Plot of speed versus separation (measured on the plane of the sky) from the 3.6 cm continuum peak for all H₂O maser spots of Fig. 2b with measured proper motions (filled circles). Also shown is a plot of the l.o.s. component of the velocity for all spots detected in this study (empty circles). Note the tendency of the speed to increase with distance from the YSO.
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$\begin{figure} \par\includegraphics[angle=-90,width=8.5cm,clip]{2685fig8.ps} \end{figure}$	Figure 8: Peak velocity of feature (1) and (2) (see Fig. 5) as a function of time. Error bars denote line FWHMs. The dashed lines are the same as in Fig. 5 and represent linear fits to the data, while dotted and solid lines are fits of the type $V\propto (t-t_0)^{-1/2}$ and $V\propto \exp[-(t-t_0)/\tau]$ , respectively.
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