\begin{table}%t1
%\begin{center}
\par
\newcommand{\lw}[1]{\smash{\lower2.ex\hbox{#1}}}
\caption{Summary of VLBA H$_2$O maser observations.}
\label{tbl:vlbaobs}
\begin{tabular}{lcccccccccc}
\hline\hline\noalign{\smallskip}
       & & \multicolumn{4}{c}{MAIN Field: Low-Velocity Emission} & & \multicolumn{4}{c}{Sub-Field$^b$: EHV Emission} \\
\cline{3-6}\cline{8-11}   
Epoch$^a$  & & Number of & $\theta_{\rm maj}\times\theta_{\min}$ & PA & Sensitivity$^c$ & & 
           Number of & $\theta_{\rm maj}\times\theta_{\min}$ & PA & Sensitivity$^c$ \\
           & & antennas  & (mas$\times$mas) & (deg) & (mJy beam$^{-1}$) & & 
               antennas  & (mas$\times$mas) & (deg) & (mJy beam$^{-1}$) \\ \hline
I   & & 10$^d$ & \multicolumn{1}{r}{0.78 $\times$ 0.40} & $-2$ & 3.4 & & 5$^f$ & 2.8 $\times$ 1.4 & $+$29 & 6.2 \\
II  & & 9$^e$  & \multicolumn{1}{r}{1.1 $\times$ 0.51} & $+26$ & 3.7 & & 5$^f$ & 2.8 $\times$ 1.5 & $+$29 & 4.7 \\
III & & 10$^d$ & \multicolumn{1}{r}{0.95 $\times $ 0.40} & $-14$ & 2.8 & & 5$^f$ & 2.9 $\times$ 1.6 & $+$24 & 4.8 \\
IV  & & 10$^d$ & \multicolumn{1}{r}{1.1 $\times $ 0.39} & $-14$ & 3.5 & & 5$^f$ & 2.9 $\times$ 1.6 & $+$27 & 6.9 \\
\hline
\end{tabular}
%\end{center}
\par
$^a$~The 4 epochs are 1999 April 1, May 5, June 5 and July 4.
$^b$~The following data are common for the Sub-Fields 1 and 2 (see Sect.~\ref{sss:ehvsearch}).
$^c$~An rms image noise level with a velocity resolution of 0.2~km~s$^{-1}$.
$^d$~All 10 VLBA stations.
$^e$~Except the North Liberty station.
$^f$~Fort Davis, Los Alamos, Pie Town, Kitt Peak and Owens Valley.
\end{table}