\begin{table}%t3
  %\centering
\par
  \caption {\label{tab:peakab}Fractional abundances of CN, HCN, HNC and \nnhp\ relative
    to H towards the dust emission peaks of our source sample.
    Tables~\ref{tab:l183}--\ref{tab:l310} give the fractional
    abundances toward all the observed positions.}
  \begin{tabular}{l c c c c c c c} 
  \hline\hline
  \noalign{\smallskip}
    Source & [CN] & [HCN] & [HNC] & [\nnhp] & [NO]\tablefootmark{a} & CN:HCN & HNC:HCN \\ %& N(\hh)
    & \tdix{-9} & \tdix{-9} & \tdix{-9} & \tdix{-10} & \tdix{-9} & \\ %& \tdix{22}~\cc
    \hline
    L~183 & 0.40 & 0.17 & 0.45 & 0.78 & 10.0 & 2.4 & 2.6\\
    L~1544 & 1.11 & 0.56 & 1.12 & 1.20 & 4.0 & 2.0 & 2.0\\
    Oph~D & 0.37 & 0.23 & 0.38 & & & 1.6 & 1.7\\
    L~1517B& 1.12 & 0.48 & 1.50 & & & 2.3 & 3.1\\
    L~310 & 4.40 & 1.50 & 2.50 & & & 2.9 & 1.6\\
    \hline
  \end{tabular}
\par
  \tablefoot {
    $\rm [X]=n(X)/2n(\hh)$. An isotopic ratio $\twc{:}\thc=68$ was
    assumed when using the \thc\ isotopologues.
    A global uncertainty (including statistical and systematic
    errors) of 40\% is assumed.
    \tablefoottext{a}{The abundance of NO is taken from A07.}}
\end{table}