\begin{table}%t4
\caption{\label{table:line_parameters}N$_2$H$^+(1{-}0)$ and N$_2$D$^+(2{-}1)$ line parameters derived from
Hanning smoothed spectra.}
%\centerline
 {
\begin{tabular}{c c c c c c c}
\hline\hline 
Line/Position & $v_{\rm LSR}$ [km s$^{-1}$] & $\Delta v$ [km s$^{-1}$] & $T_{\rm A}^*$ [K] & $\int T_{\rm A}^*(v){\rm d}v$ [K~km~s$^{-1}$] & $\tau_{\rm tot}$ & $T_{\rm ex}$ [K]\\[-3.2mm] \\
\hline
{\bf N$_{\bf 2}$H$^{\bf +}$}$(1{-}0)$\\
IRAS~05405-0117$^a$ & $9.228\pm0.001$ & $0.290\pm0.002$ & $2.37\pm0.04$ & $3.97\pm0.05$ & $6.1\pm0.03$ & $6.8\pm0.07$\\ 
Ori~B9~E$^b$ & $9.163\pm0.002$ & $0.298\pm0.005$ & $1.46\pm0.04$ & $2.26\pm0.03$ & $3.5\pm0.5$ & $6.1\pm0.3$\\ 
Ori~B9~N$^c$ & $9.149\pm0.003$ & $0.261\pm0.008$ & $1.82\pm0.09$ & $2.29\pm0.04$ & $2.2\pm0.8$ & $8.3\pm1.4$\\ 
{\bf N$_{\bf 2}$D$^{\bf +}$}$(2{-}1)$\\
IRAS~05405-0117 & $9.414\pm0.012$ & $0.319\pm0.027$ & $0.31\pm0.04$ & $0.13\pm0.01$ & $0.26\pm0.01$$^d$ & $6.8\pm0.07$\\Ori~B9~E & $9.285\pm0.013$ & $0.194\pm0.029$ & $0.27\pm0.03$ & $0.09\pm0.01$ & $0.28\pm0.03^d$ & $6.1\pm0.3$\\ 
Ori~B9~N$^e$ & $9.255\pm0.009$ & $0.136\pm0.021$ & $0.28\pm0.07$ & $0.09\pm0.01$ & $0.16\pm0.05^d$ & $8.3\pm1.4$\\ 
\hline 
\end{tabular} } 
\medskip
The integrated line intensity
($\int T_{\rm A}^*(v){\rm d}v$) includes all the
hyperfine components in the case of N$_2$H$^+$, whereas for N$_2$D$^+$ only
the main group is included.\\
$^a$ Caselli \& Myers (1994) derived $v_{\rm LSR}=9.209\pm0.003$~km~s$^{-1}$, $\Delta v=0.313\pm0.008$~km~s$^{-1}$, and $\tau_{\rm tot}=4.594\pm0.825$. 
$^b$ For the other velocity component hyperfine fit yields $v_{\rm LSR}=1.310\pm0.013$~km~s$^{-1}$, $\Delta v=0.436\pm0.035$~km~s$^{-1}$, and $\tau_{\rm tot}=6.6\pm2.0$. 
$^c$ For the other velocity component $v_{\rm LSR}=2.219\pm0.006$~km~s$^{-1}$, $\Delta v=0.378\pm0.021$~km~s$^{-1}$, $T_{\rm A}^*=0.52\pm0.03$ K, $\tau_{\rm tot}=1.0$, and $T_{\rm ex}=5.9\pm0.17$ K. 
$^d$ $\tau_{\rm tot}$ calculated by taking into account
that the main hyperfine group corresponds to 54.3\% of the total optical
depth. $\tau_{\rm main ~ group}$ is calculated using $T_{\rm MB}$ from Gaussian fit to the main group and $T_{\rm ex}$ from N$_2$H$^+(1{-}0)$. 
$^e$ For the other velocity component $v_{\rm LSR}=2.290\pm0.044$~km~s$^{-1}$, $\Delta v=0.187\pm0.090$~km~s$^{-1}$, $T_{\rm A}^*=0.22\pm0.06$~K, and $\tau_{\rm tot}=0.12\pm0.01$ ($\tau_{\rm tot}$ is calculated as described in footnote $d$).
\end{table}