\begin{table}%t4
\caption{\label{princ_lines}Principal absorption metal lines most frequently detected\protect associated with high column density absorption systems.}
\small%\centerline
{  
\begin{tabular}{l l l l}
\hline\hline\noalign{\smallskip}
Ion & $\lambda _0$ (\AA)&  \textit{f}~$^a$ & $\log\lambda _0 f  + \log[N / N($H$)]_{\odot}+12.00$  \\		 	
\noalign{\smallskip}\hline
Si~{\sc iii} 	&		1206.500		&	 0.221				&	10.87		\\
H~{\sc i}~   	&      	1215,6701		&	 0.4162				&   14.70		\\
N~{\sc v} 		&		1238.821		&	 0.152				&   10.24		\\
N~{\sc v} 		&		1242.804		&	 0.0757				&   9.93		\\
Si~{\sc ii} 	&		1260.4223		&	 0.959				&	10.65		\\
O~{\sc i} 	 	&  		1302,1685     	&    0.0486		      	&   10.67  		\\
Si~{\sc ii} 	&		1304,3702		&	 0.147				&	9.85		\\
C~{\sc ii}  	&  		1334,5323    	&    0.118		       	&   10.85   	\\
Si~{\sc iv} 	&     	1393.76018   	&    0.528	        	&   10.44		\\
Si~{\sc iv}	 	&     	1402.770   		&    0.262	        	&   10.13		\\
Si~{\sc ii} 	&     	1526,70698  	&    0.23			    &   10.11   	\\
C~{\sc iv} 		&     	1548.2041  		&    0.194      		&   11.13		\\
C~{\sc iv} 		&     	1550.7812  		&    0.097      		&   10.83		\\
Fe~{\sc ii} 	&		1608.45085		&	 0.062				&	9.52		\\
Al~{\sc ii} 	&     	1670,7886  		&    1.88			    &   9.99		\\
Al~{\sc iii} 	&     	1854.7164  		&    0.539			    &   9.49		\\
Al~{\sc iii} 	&     	1862.7895  		&    0.268			    &   9.19		\\
Fe~{\sc ii} 	& 		2344.2139		&	 0.108				&	9.92		\\
Fe~{\sc ii}		& 		2374.4162		&	 0.0395				&	9.49		\\
Fe~{\sc ii}		& 		2382.7652		&	 0.328				&	10.41		\\	
\hline\end{tabular}}
\smallskip 
 $^a$ Oscillator strengths taken from Morton (1991). 
\end{table}