\begin{table}%t1
\caption{\label{Tab:obs_log}Log of the observations.}
\par
\small%\centerline
 {
\begin{tabular}{llll}
\hline\hline
 	 		&					&					&	Total integration time 	 \\ 	 	
date			&	knots			&	slit positions$^a$	&	(min)					 \\
\hline
2003 Jan 12	&	NK1				&	perp3			&	60				 \\
			&	SK1				&	perp				&	60				 \\
2003 Jan. 13	&	NK1, NK2, NK4		&	par				&	16.7				 \\
			&	NK1				&	perp1                           &       30                                 \\
			&	NK1				&	perp2                           &       26.7                               \\
			&	NK1				&	perp4	                   &       26.7                               \\
			&	SK1, SK2, SK4		&	par				&	15				 \\
\hline
\end{tabular}}
\medskip
$^a$ Designation of the slit orientation with respect to the flow axis, ``par'' stands for parallel, ``perp'' for perpendicular, see Fig.~\ref{fig:intensity_map_slits}.
\end{table}