\begin{table}%T1
     \caption{\label{t:telescopes}Data on telescopes and receivers.}
           %\centering
\par
      \begin{tabular}{ccccc}
      \hline\hline
      Telescope & Frequency & Beamwidth & $T_{\rm rec}$ & $\eta_{\rm mb}$ \\
                & [MHz]     & [$\arcsec$] & [K] \\
      \hline
      OSO   &  86847 & 42 & 150  & 0.55 \\
      SEST  &  86847 & 57 & 100  & 0.75 \\
      SEST  & 130269 & 39 & 120  & 0.65 \\
      IRAM  & 130269 & 18 & 150  & 0.58 \\
      SEST  & 217105 & 25 & 600  & 0.55 \\
      SEST  & 260518 & 21 & 800  & 0.45\\
      \hline
      \end{tabular}
 \end{table}