\begin{table}%t3
\caption{\label{t3} Astrometric calibration.}
%\centerline
{\begin{tabular}{lllllll}
\hline\hline
Astrometric    & Date          & Scale          & $\sigma$(Scale) & Orientation & $\sigma$(Orientation) & Corrected stars \\
standard field &               & ($\arcsec$/px) &  ($\arcsec$/px)  & ($\degr$)   & ($\degr$)             & HIP Nr          \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
NGC~6611  & 17 May 2001    & 0.499 & 0.001 & 0.35 & 0.01 & 79492, 83020, 83988/96, 86282,    \\
          &                &       &       &      &      & 87768, 91768/72, 94336, 97241,    \\
          &                &       &       &      &      & 97292, 106694, 110893             \\
NGC~6611  & 5 June 2001    & 0.499 & 0.001 & 0.21 & 0.01 & 54952, 56809, 63253, 65011/12,    \\
          &                &       &       &      &      & 65343, 66492, 67422               \\
NGC~6611  & 22 August 2002 & 0.498 & 0.001 & 0.39 & 0.01 & 473, 2552, 3937, 10531/29, 13642, \\
          &                &       &       &      &      & 15844, 17666, 17749/50, 18512,    \\
          &                &       &       &      &      & 21088, 66077, 110526, 110640      \\
\hline
\end{tabular}}
\end{table}