\begin{table}%t4
%\centering
\par
\caption{N$_2$H$^+$(1--0) line parameters with optical depths.}
\small
\begin{tabular}{lrrrrrr}
\hline\hline
Source ($\Delta \alpha \arcsec$, $\Delta \delta \arcsec$)
       & $T_{\rm EX}$(12--12) & $T_{\rm EX}$(23--12) & $T_{\rm EX}$(01--12)  & $V_{\rm LSR}$(23--12) & $\Delta V$   & $\tau$(23--12)  \\
       &      (K)             &      (K)             &       (K)             &  (km s$^{-1}$)        & (km s$^{-1}$) \\
\noalign{\smallskip}\hline\noalign{\smallskip}
\par
RNO~1B (0,0)        & 7.75(0.37) & 9.18(0.38) & 7.32(0.50) & --17.54(0.01) & 1.94(0.06) & 1.0(0.1) \\
S~255 (0,60)        &  9.3(1.6)  & 10.6(1.6)  & 10.1(2.2)  &    8.96(0.02) & 2.31(0.10) & 0.5(0.2) \\
S~76E (--20,--20)   & 24.4(4.2)  & 27.0(4.3)  & 27.1(5.4)  &   32.44(0.01) & 2.86(0.06) & 0.3(0.1) \\
DR~21 (0,--40)      & 20.3(1.3)  & 22.8(1.3)  & 25.0(2.1)  &  --3.25(0.01) & 3.09(0.04) & 0.6(0.1) \\
S~140 (60,20)       & 21.4(3.7)  & 25.4(4.1)  & 27.0(5.5)  &  --7.03(0.01) & 1.62(0.05) & 0.4(0.1) \\
G~270.26$+$0.83 (--20,20) & 8.8(1.5) & 9.2(1.5) & 8.8(1.8) &    9.69(0.02) & 3.17(0.08) & 0.3(0.1) \\
G~291.27$-$0.71 (--80,--100)& 24.2(6.0) & 25.9(6.2) & 29.1(7.7) & --24.36(0.01) & 2.90(0.03) & 0.15(0.05) \\
G~316.77$-$0.02 (240,--60)  &  8.9(0.6) & 10.1(0.6) & 10.1(0.9) & --37.94(0.01) & 3.61(0.06) & 0.5(0.1) \\
G~345.01$+$1.80 (--20,20) & 11.8(0.3) & 14.3(0.3) & 13.4(0.5)   & --14.07(0.01) & 3.08(0.02) & 0.62(0.03) \\
G~351.41$+$0.64 (20,100)  & 16.3(0.3) & 18.2(0.2) & 20.6(0.5)   & --4.20(0.01)  & 3.65(0.02) & 0.86(0.03) \\
\hline
\end{tabular}
\label{table:optdepth}
\end{table}