**Table 4:** Position shifts and proper motions for the 7 maser features.
$\begin{displaymath}\begin{tabular}{lr@{$~\pm~$}l r@{$~\pm~$}l r@{$~\pm~$}l r@{$~... ....9 & 5.2 & $-$91.3 & 29.5 & 79.4 & 0.2 \\ \hline \end{tabular}\end{displaymath}$ ^a and ^b total position shifts of the maser features over the observing period, namely per 95 days, along RA and Dec directions, respectively, derived from the least-square fitting in Fig. 7. ^c $\vert\mu\vert=\sqrt{(\Delta\alpha)^2+(\Delta\delta)^2}$ . For the maser features where we could not detect well-defined proper motions, apparent position shifts are given in the parenthesis. ^d Position Angle of the proper motion vector in the plane of the sky. ^e Transverse velocity on the plane of the sky converted from $\vert\mu\vert$ . ^f 3-Dimensional velocity obtained from $V_{\rm 3D}=\sqrt{V_{\rm trans}^2+(V_{\rm mean}-V_{\rm ref})^2}$ where $V_{\rm mean}$ is in Table 3 and $V_{\rm ref}$ is the LSR-velocity of the reference spot (1.6 km s^-1). Negative and positive represent approaching and receding motions, respectively. ^g Inclination angle of the $V_{\rm 3D}$ vector with respect to the plane of the sky, obtained from $i=\tan^{-1}(\vert V_{\rm mean}-V_{\rm ref}\vert/V_{\rm trans})$ . ^h All the parameters for Feature 2 are derived from the data taken in the first 3 epochs.

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