\begin{table}%t2
\caption{\label{tab2}Line widths and optical depths of HC$_3$N transitions (see Sect.~4.1.1)$^{ a}$.}
\par
%
\par
%\centerline
{
\begin{tabular}{cccc}
\hline\hline 
  Line                         &      $FWHP$      & $\tau_{\rm peak}$ & $\int{\tau {\rm d}V}$ \\
\hline
HC$_3$N $J=3 \leftarrow 2$     & $10.6\pm1.2$   & $0.0057\pm0.0008$ &    $0.060\pm0.005$    \\
HC$_3$N $J=4 \leftarrow 3$     & $ 9.3\pm1.0$   & $0.0131\pm0.0018$ &    $0.121\pm0.010$    \\
HC$_3$N $J=5 \leftarrow 4$     & $ 8.6\pm1.0$   & $0.0211\pm0.0031$ &    $0.181\pm0.017$    \\
HC$_3$N $J=6 \leftarrow 5$     & $ 9.0\pm1.9$   & $0.0280\pm0.0069$ &    $0.251\pm0.034$    \\
HC$_3$N $J=7 \leftarrow 6$     & $12.2\pm2.1$   & $0.0173\pm0.0035$ &    $0.210\pm0.024$    \\
HC$_3$N $J=10\leftarrow 9$     &     --	        &       --	        &        $<$0.235       \\
\hline
\end{tabular}}
 \medskip
\par
$^a$ Full Width to Half Power ($FWHP$) line widths, peak apparent optical depths, and integrated 
optical depths obtained from one component Gaussian fits. The upper limit to the HC$_3$N 
$J =10 \leftarrow 9$ integrated opacity is a 3$\sigma$ value. 
\end{table}