\begin{table}%tb1
\caption{The confusion limit reached by the IRAM 30-m telescope
toward some molecular line sources.}
%\centerline
{
\begin{tabular}{r r r r  r}
\hline \hline 
Source &$\lambda$& Weakest &~$t_{\rm int}^{a}$ & Ref.$^b$\\
$\Delta v$&&detect. lines& & \\
&mm&mK&  h & \\
\hline IRC+10216 & 3 & 1.5 &  28&1)\\
28~km~s$^{-1}$&2&3.5&10 &1, 2) \\
& 1.3 &~$\la$$2$& 80&2)\\
\hline
 Orion-KL& 3 & 20 & 0.8&3)\\
5~km~s$^{-1}$& 2 & 50 &0.3 &4) \\
&1.3&70 &0.4&3)\\
\hline SgrB2(N)& 3 &~$\sim$$20$ & 0.4& 3)\\
$\sim$17~km~s$^{-1}$& 2 &~$\sim$$30$ & 0.4 &3) \\
& 1.3&~$\sim$$40$  & 0.5&3) \\
\hline
\end{tabular}}
\smallskip
$^a$  Integration time (on+off) with present receivers at the IRAM
30-m telescope under normal winter conditions (good summer
conditions), one polarization to obtain an rms of~1/3~$T_{\rm mb}$
with a velocity resolution of~1/5 the line width (one polarization
receiver only).\\ 
$^b$~References: 1)~this paper 2)~Ziurys et~al.
(\cite{ziurys2002}); 3)~unpublished data; 4)~Mauersberger et~al.
(\cite{mau88}).\\  
$^c$~Weaker lines can be identified if one makes
use of the unique line shapes of the spectra of this source
(Cernicharo et~al. \cite{cerni2004}).
\end{table}