All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{1658fig1.eps} \end{figure}$ Figure 1: Stellar optical light curve of TX Cam (courtesy of AAVSO). The vertical dashed lines in the plot represent the times of the four epochs of VLBA observations. The downward triangles indicate upper limits to the optical magnitudes.
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In the text

$\begin{figure} \par\subfigure[Epoch~I]{\includegraphics[width=8.7cm,clip]{1658fi... ...gure[Epoch~IV]{\includegraphics[width=8.7cm,clip]{1658fig2d.eps} } \end{figure}$ Figure 2: The v = 1 contour (green) maps aligned with v = 2 contour (red) maps at four epochs. In Epochs III and IV the "R'' indicates the feature used for registration. Epoch I: for v = 1 contours cover irregularly the range between 0.38-10.98 Jy/beam and for v = 2 from 0.79-29.13 Jy/beam. Epoch II: for v = 1 contours cover the range between 0.83-7.85 Jy/beam and for v = 2 from 1.66-18.65 Jy/beam. Epoch III: For v = 1 contours cover the range between 0.85-39.98 Jy/beam and for v = 2 from 0.90-75.06 Jy/beam. Epoch IV: for v = 1 contours cover the range between 1.62-80.75 Jy/beam and for v = 2 from 1.90-94.93 Jy/beam.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.8cm]{1658fig3a_new.ps} \hspace... ... \hspace{0.2cm} \includegraphics[width=8.8cm]{1658fig3d_new.ps} } \end{figure}$ Figure 3: VLBI maps of v = 1, J = 1-0 ( upper) and v = 2, J = 1-0 ( lower) SiO maser emission toward TX Cam, summed over all channels of emission, observed at Epoch III ( left) and at Epoch IV ( right). The colour bar shows the flux scale in Jy/beam.
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In the text

$\begin{figure} \par\includegraphics[width=18cm]{aa1658f4.eps} \end{figure}$ Figure 4: Left: velocity field of the masers in the v = 1 line of TX Cam observed at Epoch III. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 top left for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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In the text

$\begin{figure} \includegraphics[width=18cm]{aa1658f5.eps} \end{figure}$ Figure 5: Left: velocity field of the masers in the v = 2 line of TX Cam observed at Epoch III. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 bottom left for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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In the text

$\begin{figure} \par\includegraphics[width=18cm]{aa1658f6.eps} \end{figure}$ Figure 6: Left: velocity field of the masers in the v = 1 line of TX Cam observed at Epoch IV. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 top right for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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In the text

$\begin{figure} \par\includegraphics[width=18cm]{aa1658f7.eps} \end{figure}$ Figure 7: Left: velocity field of the masers in the v = 2 line of TX Cam observed at Epoch IV. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 bottom right for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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In the text

$\begin{figure} \par\includegraphics[width=8.7cm,clip]{1658fig8.eps} \end{figure}$ Figure 8: The integrated flux of the v=1 maser emission (solid line) and v=2 maser emission (dashed line) per annulus at Epoch III. The intensity of the maps was logarithmically scaled prior to the analysis. The inset represents the normalised cumulative flux versus radius of the two masers. The vertical lines in the inset indicate the radii of the maser ring containing 50% of the total emission.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{1658fig9.eps} \end{figure}$ Figure 9: The integrated flux of the v=1 maser emission (solid line) and v=2 maser emission (dashed line) per annulus at Epoch IV. The intensity of the maps was logarithmically scaled prior to the analysis. The inset represents the normalised cumulative flux versus radius of the two masers. The vertical lines in the inset indicate the radii of the maser ring containing 50% of the total emission.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{1658fig10.eps} \end{figure}$ Figure 10: Spoke geometry and possible mechanism for preferentially detecting slightly red- and blue-shifted spokes. The rectangles indicate spokes of gas flowing out from the star at different angles around the shell $\theta$ . The thick line rectangles are the brightest spokes which we observe. All spokes have the same velocity field which is decelerating with radius. The line of sight through a spoke in the sky plane (at $\theta =0$ ), indicated by LOS1, has a velocity coherent path equal to the spoke width. As we go around the shell in angle $\theta$ the coherent paths through spokes increases proportional to $1/\cos(\theta)$ . At some point around the shell, the line of sight through a spoke, indicated by LOS2, has a maximum velocity coherence length. This occurs where the change in velocity along this LOS equals the gas internal velocity dispersion. Further around the shell, such as the spoke crossed by LOS3, the velocity coherent path length decreases because of the large velocity gradient along the path. Slightly red- and blue-shifted spokes, such as those crossed by LOS2, which have the largest coherent paths will be brightest and most easily detected.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{1658fig1.eps} \end{figure}$	Figure 1: Stellar optical light curve of TX Cam (courtesy of AAVSO). The vertical dashed lines in the plot represent the times of the four epochs of VLBA observations. The downward triangles indicate upper limits to the optical magnitudes.
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$\begin{figure} \par\mbox{\includegraphics[width=8.8cm]{1658fig3a_new.ps} \hspace... ... \hspace{0.2cm} \includegraphics[width=8.8cm]{1658fig3d_new.ps} } \end{figure}$	Figure 3: VLBI maps of v = 1, J = 1-0 ( upper) and v = 2, J = 1-0 ( lower) SiO maser emission toward TX Cam, summed over all channels of emission, observed at Epoch III ( left) and at Epoch IV ( right). The colour bar shows the flux scale in Jy/beam.
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$\begin{figure} \par\includegraphics[width=18cm]{aa1658f4.eps} \end{figure}$	Figure 4: Left: velocity field of the masers in the v = 1 line of TX Cam observed at Epoch III. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 top left for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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$\begin{figure} \includegraphics[width=18cm]{aa1658f5.eps} \end{figure}$	Figure 5: Left: velocity field of the masers in the v = 2 line of TX Cam observed at Epoch III. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 bottom left for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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$\begin{figure} \par\includegraphics[width=18cm]{aa1658f6.eps} \end{figure}$	Figure 6: Left: velocity field of the masers in the v = 1 line of TX Cam observed at Epoch IV. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 top right for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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$\begin{figure} \par\includegraphics[width=18cm]{aa1658f7.eps} \end{figure}$	Figure 7: Left: velocity field of the masers in the v = 2 line of TX Cam observed at Epoch IV. Horizontal colour bar gives mean LSR velocity at each position. Compare to Fig. 3 bottom right for the corresponding integrated intensity map. Right: spectrum of the integrated flux density from all the maser emission in the map (dashed line) together with the total power spectrum (solid line).
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