\begin{table}%t3
\caption{\label{tobs}Observed lines.}
%\centering
\par
\begin{tabular}{cccc}
\hline\hline \noalign{\smallskip}
Line & Frequency & $T_{\rm sys}$ & 1$\sigma$ rms\tablefootmark{a} \\
 & (GHz) & (K) & (K)\\
\hline
HCO$^{+}$(1--0) & 89.188516 & 144 & 0.48\\ 
HCN(1--0) & 88.632176 & 166 & 0.55\\
C$^{18}$O(2--1) & 219.560328 & 749 & 3.5\\
\hline
\end{tabular}
\tablefoot {\tablefoottext{a}{Average 1$\sigma$ rms of a single spectrum after smoothing is to a resolution of 0.5~km~s$^{-1}$.}}
\end{table}