\begin{table}%t1
 %\centering
\par
 \caption{\label{table_positions}Coordinates of observed sources.}
\par
\begin{tabular}{lccc}
\hline\hline\noalign{\smallskip}
\multicolumn{1}{c}{Source} & \multicolumn{1}{c}{$\alpha_{{\rm J}2000.0}$} & \multicolumn{1}{c}
{$\delta_{{\rm J}2000.0}$} & \multicolumn{1}{c}{$V_{\rm LSR}$ (km~s$^{-1}$)}\\  
\hline\noalign{\smallskip}
Sgr B2(M) \hfill & $17^{\rm h}47^{\rm m}20.4^{\rm s}$ & $-28^{\circ}23^{\prime}07^{\prime\prime}$ & $+62$\\
Sgr B2(N) \hfill & $17^{\rm h}47^{\rm m}20.0^{\rm s}$ & $-28^{\circ}22^{\prime}19^{\prime\prime}$ & $+64$\\
Sgr B2(S)\hfill & $17^{\rm h}47^{\rm m}20.5^{\rm s}$ & $-28^{\circ}23^{\prime}45^{\prime\prime}$ & $+61$\\
Sgr B2(M)(20$^{\prime\prime}$,~100$^{\prime\prime}$) \hfill & $17^{\rm h}47^{\rm m}21.9^{\rm s}$ & $-28^{\circ}21^{\prime}27^{\prime\prime}$ & $+68$\\
Sgr B2(M)($-$40$^{\prime\prime}$,~0$^{\prime\prime}$) \hfill & $17^{\rm h}47^{\rm m}17.4^{\rm s}$ & $-28^{\circ}23^{\prime}07^{\prime\prime}$ & $+54$\\
Sgr B2(M)(20$^{\prime\prime}$,~$-$180$^{\prime\prime}$) \hfill & $17^{\rm h}47^{\rm m}21.9^{\rm s}$ & $-28^{\circ}26^{\prime}07^{\prime\prime}$ & $+50$\\
\hline
\end{tabular}
\end{table}