\begin{table}%t3 \caption{\label{hyd_tab}Parameters of VLBA 1.665~GHz hydroxyl maser features.} %\centering \par \begin{tabular}{c c c c c c r r c c c} \hline \hline \noalign{\smallskip} Feature & \multicolumn{2}{c}{$V_{\rm LSR}$ } & \multicolumn{2}{c}{$F_{\rm peak}$} & & \multicolumn{1}{c}{$\Delta x$} & \multicolumn{1}{c}{$\Delta y$} & & $\Delta V_{\rm z}$\tablefootmark{a} & $B_{\rm z}$ \\ & \multicolumn{2}{c}{(km s$^{-1}$)} & \multicolumn{2}{c}{(Jy beam$^{-1}$)} & & \multicolumn{1}{c}{(mas)} & \multicolumn{1}{c}{(mas)} & & (km s$^{-1}$) & (mG) \\ & RCP & LCP & RCP & LCP & & & & & & \\ \hline 1 & 70.88 & 71.76 & 2.39 & 0.40 & &$ 0 $ & $ 0 $ & & $ -0.86 $ & $ -1.5 $ \\ 2 & 67.89 & ... & 2.02 & ... & &$ -210.26 \pm 1.07 $ & $ 178.74 \pm 0.77 $ & & ... & ... \\ 3 & 66.84 & 66.84 & 1.36 & 0.84 & &$ 14.24 \pm 0.62 $ & $ 18.87 \pm 0.77 $ & & ... & ... \\ 4 & 73.87 & 73.87 & 1.01 & 0.16 & &$ -251.52 \pm 0.78 $ & $ 88.39 \pm 1.47 $ & & ... & ... \\ 5 & ... & 74.75 & ... & 0.97 & &$ -385.08 \pm 1.46 $ & $ 203.14 \pm 1.00 $ & & ... & ... \\ 6 & ... & 70.57 & ... & 0.89 & &$ 199.12 \pm 1.45 $ & $ 174.08 \pm 1.13 $ & & ... & ... \\ 7 & 68.07 & ... & 0.74 & ... & &$ -185.97 \pm 0.67 $ & $ 191.75 \pm 1.29 $ & & ... & ... \\ 8 & 72.99 & 72.99 & 0.67 & 0.26 & &$ 57.29 \pm 0.71 $ & $ 119.21 \pm 0.94 $ & & ... & ... \\ 9 & ... & 75.10 & ... & 0.60 & &$ -297.88 \pm 1.46 $ & $ 130.40 \pm 1.14 $ & & ... & ... \\ 10 & 74.92 & ... & 0.55 & ... & &$ -358.64 \pm 1.31 $ & $ -170.67 \pm 1.14 $ & & ... & ... \\ 11 & 70.35 & 69.82 & 0.52 & 0.23 & &$ 56.12 \pm 0.94 $ & $ 114.09 \pm 1.10 $ & & $ +0.62 $ & $ +1.0 $ \\ 12 & 67.19 & ... & 0.46 & ... & &$ 45.90 \pm 0.66 $ & $ 111.93 \pm 0.98 $ & & ... & ... \\ 13 & 76.33 & 79.67 & 0.25 & 0.43 & &$ -223.40 \pm 1.45 $ & $ 71.08 \pm 1.20 $ & & $ -3.41 $ & $ -5.8 $ \\ 14 & ... & 76.33 & ... & 0.41 & &$ 366.46 \pm 1.57 $ & $ -149.68 \pm 1.13 $ & & ... & ... \\ 15 & 68.77 & ... & 0.38 & ... & &$ 52.32 \pm 2.18 $ & $ 113.99 \pm 1.27 $ & & ... & ... \\ 16 & ... & 63.50 & ... & 0.31 & &$ 32.32 \pm 1.56 $ & $ 108.87 \pm 1.73 $ & & ... & ... \\ 17 & 64.90 & ... & 0.30 & ... & &$ 39.23 \pm 1.10 $ & $ 111.08 \pm 1.12 $ & & ... & ... \\ 18 & 70.18 & ... & 0.25 & ... & &$ 192.37 \pm 1.33 $ & $ 175.05 \pm 1.53 $ & & ... & ... \\ 19 & 79.32 & 77.21 & 0.25 & 0.17 & &$ -321.93 \pm 0.90 $ & $ 130.00 \pm 2.23 $ & & $ +2.11 $ & $ +3.6 $ \\ 20 & 64.55 & 65.08 & 0.23 & 0.13 & &$ 37.16 \pm 0.92 $ & $ 108.63 \pm 1.33 $ & & $ -0.49 $ & $ -0.8 $ \\ 21 & 66.84 & ... & 0.22 & ... & &$ -134.66 \pm 0.91 $ & $ 147.73 \pm 1.29 $ & & ... & ... \\ 22 & 62.62 & 62.79 & 0.16 & 0.20 & &$ 26.50 \pm 1.98 $ & $ 106.74 \pm 1.81 $ & & ... & ... \\ 23 & 69.65 & 69.30 & 0.18 & 0.19 & &$ 17.17 \pm 1.78 $ & $ 18.23 \pm 2.17 $ & & ... & ... \\ 24 & 60.68 & 60.51 & 0.12 & 0.14 & &$ 20.64 \pm 1.70 $ & $ 70.44 \pm 2.47 $ & & ... & ... \\ \hline \noalign{\smallskip} \multicolumn{11}{c}{Reference Feature: Absolute position}\\ Feature & \multicolumn{4}{c}{RA(J2000)} & \multicolumn{4}{c}{ Dec(J2000) } & & \\ & \multicolumn{4}{c}{(h m s)} & \multicolumn{4}{c}{(\degr $'$ $''$)} & & \\ \hline 1 &\multicolumn{4}{c}{18:34:40.28515 $\pm$ 0.00026}&\multicolumn{4}{c}{$-$09:00:38.3783 $\pm$ 0.0044} & & \\ \hline \end{tabular} \tablefoot {For each identified feature, the label (given in Col.~1) increases with decreasing brightness. Columns~2(3) and~4(5) report the LSR velocity and brightness of the brightest spot for the right (left) circular polarization. Columns~6 and~7 give the position offset relative to the feature~\#1, in~the east and north directions, respectively. Columns~8 and~9 report the fit split of LSR velocity (RCP-LCP) between co-spatial circular polarization components and the inferred l.o.s. magnetic field strength, respectively. The absolute position of the reference feature~\#1 is reported at the bottom of the table. \\ \tablefoottext{a}{A magnetic field of 0.34~mG shifts the emission velocity of 1665~MHz OH~masers by 0.2~km~s$^{-1}$.}} \end{table}