\begin{table}%t5
%\centering
\par
\caption{Velocity gradient derived through a linear fit to the
centroid of the brightness for each velocity channel as indicated in
Fig.~\ref{pvdia}.\label{posveltab}}
\begin{tabular}{ll}\hline\hline
Molecule & Velocity gradient \\
         & [km~s$^{-1}$ arcsec$^{-1}$]\\ \hline
CS       & $1.09\pm 0.29$    \\
HCN      & $1.00\pm 0.49$    \\
HCO$^+$   & $1.25\pm 0.53$    \\ \hline
\end{tabular}
\end{table}