\begin{table}%t1
\caption{\label{tab:lines}Observed lines in AFGL 2591.}
\par
%\centering
\par
\begin{tabular}{lllc|cccc|ccc|rr}
\hline
\hline \\[-3.4mm]
%\noalign{\smallskip}
\multicolumn{4}{l|}{Species/Transition/Electronic state/Line components\tablefootmark{f}}      & Frequency    &  $E_{u}$ & $A_{\rm ul}$   &  $T_{\rm obs}$\tablefootmark{e} &  $\int T {\rm d} v$ & $\int \tau {\rm d} v$  & $T_{\rm rms}$ &  $N^{\rm upper}({\rm X})$ &  $N^{\rm lower}({\rm X})$ \\
   &                   &       & & [GHz]        &  [K]     & [s$^{-1}$] &  [min] & [K km s$^{-1}$] & [km s$^{-1}$]   & [mK]     &        [cm$^{-2}$]    & [cm$^{-2}$]         \\
\hline \\[-3.5mm]
%\noalign{\smallskip}
CH &$J_{F,P}=3/2_{2,-}{-}1/2_{1,+}$                        & $^{2}\Pi$                & 3       &  536.7611    &  25.76   &  6.4($-$4) & 4.2& 3.46 $\pm$ 0.04\tablefootmark{a}& \ldots             &    16        &    3.0(12)       &      \ldots     \\
CH &$J_{F,P}=5/2_{3,+}{-}3/2_{2,-}$                        & $^{2}\Pi$                & 3       & 1661.1074    & 105.48   &  3.8($-$2) &20.2&  ${<}0.93$          & ${<}0.34$\tablefootmark{b,c}      &   220        &  ${<}1.3(11)$      &  ${<}2.6(12)$     \\
CH$^+$ &$J=1{-}0$                                          & $^{1}\Sigma^+$           & 1       &  835.1375    &  40.08   &  6.4($-$2) &40.4&  $0.91\pm0.03$\tablefootmark{d}& $32.63\pm0.06$\tablefootmark{d} &   16         &    1.9(11)\tablefootmark{d}   &      9.3(13)\tablefootmark{d}\\
CH$^+$ &$J=2{-}1$                                          & $^{1}\Sigma^+$           & 1       & 1669.2813    & 120.19   &  6.1($-$2) &40.4&     $3.7\pm0.2$   & \ldots             &   115        &    3.3(11)       &      \ldots     \\
o-H$_2$O$^+$ &$N_{K_aK_b,J}=1_{11,3/2}{-}0_{00,1/2}$       & $^{2}B_1$                & 5       & 1115.2041    &  53.51   &  3.1($-$2) &39.2&   \ldots          & $7.65\pm0.05$      &    33        &      \ldots      &    1.6(13)      \\
o-H$_2$O$^+$ &$N_{K_aK_b,J}=2_{02,3/2}{-}1_{11,3/2}$       & $^{2}B_1$                & 7       &  746.26      &  89.33   &  5.5($-$4) &40.6&  ${<}0.16$          & ${<}0.52$            &    25        &  ${<}2.6(11)$      &  ${<}3.0(13)$     \\
OH$^+$ &$N_{J,F}=1_{1,3/2}{-}0_{1,3/2}$                    & $^{3}\Sigma^-$           & 4       & 1033.1186    &  49.58   &  1.8($-$2) &40.6&   \ldots          &$21.98\pm0.06$      &    32        &      \ldots      &    1.1(14)      \\
OH$^+$ &$N_{J,F}=2_{1,3/2}{-}1_{1,3/2}$                    & $^{3}\Sigma^-$           & 4       & 1892.2271    & 140.39   &  5.9($-$2) &21.0&  ${<}0.83$          & ${<}0.28$            &   210        &  ${<}8.2(10)$      &  ${<}2.5(12)$     \\
NH &$N_{J,F_1,F}=1_{2,5/2,7/2}{-}0_{1,3/2,5/2}$          & $^{3}\Sigma^-$           & 21      &  974.4784    &  46.77   &  6.9($-$3) & 7.0&   \ldots          & $3.90\pm0.09$      &    43        &      \ldots      &    2.9(13)      \\
NH &$N_{J,F_1,F}=1_{1,3/2,5/2}{-}0_{1,3/2,5/2}$          & $^{3}\Sigma^-$           & 21      &  999.9734    &  47.99   &  5.2($-$3) &38.8&   \ldots          & $3.99\pm0.05$      &    29        &      \ldots      &    5.0(13)      \\
NH$^+$ &$J_{P}=3/2_{-}{-}1/2_{+}$                          & $^{2}\Pi$                & 5       & 1012.5400    &  48.59   &  5.4($-$2) &38.8&  $<0.16$          & ${<}0.19$            &    30        &  ${<}5.9(9)$       &  ${<}1.7(10)$     \\
NH$^+$ &$J_{P}=3/2_{+}{-}1/2_{-}$                          & $^{2}\Pi$                & 7       & 1019.2107    &  48.91   &  5.5($-$2) &40.6&  ${<}0.12$          & ${<}0.13$            &    22        &  ${<}4.4(9)$       &  ${<}1.2(10)$     \\
SH$^+$ &$N_{J,F}=1_{2,5/2}{-}0_{1,3/2}$                    & $^{3}\Sigma^-$           & 3       &  526.0479    &  25.25   &  9.6($-$4) & 4.2&  ${<}0.083$         & ${<}0.53$            &    11        &  ${<}4.7(10)$      &  ${<}4.5(12)$     \\
\hline
\end{tabular}
\tablefoot {The frequency is given for the strongest fine/hyperfine component. The velocity integrated intensity or absorption is summed over all fine/hyperfine components. $A(B) \equiv A$~$\times$~$10^B$. \\
\tablefoottext{a}{$1 \sigma \equiv \sqrt{\Delta V \delta v} T_{\rm rms}$, with $\Delta V \sim 10$~km~s$^{-1}$ (expected line width) and the channel width~$\delta v$ (corresponding to~1.1~MHz);}
\tablefoottext{b}{$1 \sigma \equiv \sqrt{\Delta V \delta v} T_{\rm rms} / T_{\rm cont}$;} \tablefoottext{c}{non-detections are given by the $3 \sigma$~value;}
\tablefoottext{d}{emitting or absorbing part only;} 
\tablefoottext{e}{total integration time (on+off);} 
\tablefoottext{f}{hyperfine or fine structure.}}
\vspace*{2mm}
\end{table}