\begin{table}%T1
\caption{\label{tab1}Observed and derived physical parameters.}
%\centering
\par
\begin{tabular}{lc}
\hline\hline
\noalign{\smallskip}
Velocity interval (\ks)  & $-50$ to $-40$\\
Systemic velocity (\ks) & $-45 \pm 2$\\
Kinematical distance (kpc) & $3 \pm 0.6$\\
Expansion velocity (\ks) & 7\\
Average angular radius  of the HI~shell (arcmin) & 25\\ 
Linear radius  of the HI~shell (pc) & 22\\ 
Missing HI~ mass ($M_\odot$)& $\sim$1200\\ 
Shell HI~mass ($M_\odot$)& $\sim$1950\\
Swept-up HI~mass ($M_\odot$)& $\sim$1600\\
Dynamical age (yr) & $1.7 \times 10^{6}$\\
Kinetic energy (ergs) & $8 \times 10^{47}$\\ 
\hline
\end{tabular}
\end{table}