\begin{table} %t5 %online
\caption{Calibration sources used for the JCMT observations.}\label{moldisks:calibration_sources}
\par
%\centerline
{
\begin{tabular}{lllll}
\hline
\hline
\noalign{\smallskip}
\multicolumn{1}{c}{Line}&\multicolumn{1}{c}{LkCa15}&\multicolumn{1}{c}{\object{TW~Hya}}&\multicolumn{1}{c}{\object{HD~163296}}&\multicolumn{1}{c}{MWC 480}\\
\hline
\noalign{\smallskip}
$^{12}$CO $J\!=\!3\!\rightarrow\!2$                   &\object{N2071 IR} &\object{N2071 IR}&\object{IRC+10216}&\object{W3(OH)} \\
                                                      &                  &\object{IRC+10216}                 &\object{IRAS16293-2422}&\\
$^{13}$CO $J\!=\!3\!\rightarrow\!2$                   &\object{W3(OH)} &\object{IRC+10216} &\object{NGC6334I}& \object{W3(OH)}\\
                                                      & & &\object{G34.3}& \\
                                                      & & &\object{IRAS16293-2422}\\
C$^{18}$O $J\!=\!2\!\rightarrow\!1$                   & \object{CRL618}&\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} \\
C$^{18}$O $J\!=\!3\!\rightarrow\!2$                   &\object{W3(OH)} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} & \multicolumn{1}{c}{...}\\
                                                      & &                  & & \object{N1333IR4}\\
HCO$^+$ $J\!=\!4\!\rightarrow\!3$                     &\object{W3(OH)} &\object{N2071 IR} &\object{G34.3}& \object{W3(OH)}\\
H$^{13}$CO$^+$ $J\!=\!4\!\rightarrow\!3$              &\object{IRC+10216}&\object{IRC+10216}&\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} \\ 
                                                      &                  &\object{N2071 IR}& & \\ 
DCO$^+$ $J\!=\!5\!\rightarrow\!4$                     &\object{N1333IR4}&\object{IRAS16293-2422}&\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...}\\
                                                      &\object{IRC+10216}&                      & &\\
CN $J\!=\!3\frac{7}{2}\!\rightarrow\!2\frac{5}{2}$    &\object{CRL618} &\object{CRL618} &\object{CRL618} &\object{CRL618} \\
                                                      &                &                &\object{IRAS16293-2422}&\object{G34.3}\\
HCN $J\!=\!4\!\rightarrow\!3$                         &\object{CRL618} &\object{IRC+10216} &\object{IRAS16293-2422} &\object{W3(OH)}\\
                                                      & &                   &                        &\object{CRL618}\\  
                                                      & &                   &                        &\object{OMC1}\\    
HNC $J\!=\!4\!\rightarrow\!3$                         &\multicolumn{1}{c}{...} &\object{N2071 IR} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} \\
DCN $J\!=\!5\!\rightarrow\!4$                         &\multicolumn{1}{c}{...} &\object{N2071 IR}&\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} \\  
                                                      & &\object{IRC+10216}& & \\
H$^{13}$CN $J\!=\!4\!\rightarrow\!3$                  & \multicolumn{1}{c}{not available}&\multicolumn{1}{c}{...}&\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...}\\                                                    & &\object{IRAS16293-2422}& & \\
CS $J\!=\!7\!\rightarrow\!6$                          &\multicolumn{1}{c}{not observed}&\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{not observed} \\
SO $J\!=\!8_8\!\rightarrow\!7_7$                      &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} & \multicolumn{1}{c}{...}&\multicolumn{1}{c}{...} \\
H$_{\rm 2}$CO $J\!=\!3_{12}\!\rightarrow\!2_{11}$     &\multicolumn{1}{c}{...} &\object{N2071 IR} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} \\
H$_{\rm 2}$CO $J\!=\!5_{15}\!\rightarrow\!4_{14}$     &\object{CRL618} &\object{N2071 IR} &\object{IRAS16293-2422} & \object{CRL618}\\
                                                      & &\object{IRC+10216}& & \\
CH$_{\rm 3}$OH $J\!=\!7_K\!\rightarrow\!6_K$          &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{not observed} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{...} \\
N$_{\rm 2}$H$^+$  $J\!=\!4\!\rightarrow\!3$           &\multicolumn{1}{c}{not available} &\multicolumn{1}{c}{not available} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{not available} \\
H$_{\rm 2}$D$^+$  $J\!=\!1_{10}\!\rightarrow\!1_{11}$ &\multicolumn{1}{c}{not available} &\multicolumn{1}{c}{not available} &\multicolumn{1}{c}{...} &\multicolumn{1}{c}{not avaialble} \\
\hline
\end{tabular}}
\smallskip
  {\it Note.} When a observation is carried out over more than one
  run, different standard sources are used depending on their
  availability. The entry ... indicates that the source was not
  observed in that particular line (cf.\ Table
  \ref{moldisks:intensities}), so no standard was needed.
\end{table}