\begin{table}%t1
\caption{\label{calibrators}Calibrators used for the observations of $\eta$~Ser.}
 %\centerline
{\small
      \begin{tabular}{lccccc}
        \hline \hline
        Star & $m_V$ & $m_{K{\rm s}}$ & Spect.  & $\theta_{\rm UD(K)}$ 
        & $\gamma$ \\
         & & & & (mas) & ($^\circ$)\\
        \hline
        \noalign{\smallskip}
        \object{IRC+00339}& 5.5 & 2.6 & K2III    & $1.402\pm0.018$ &  6.8\\
        \object{HR 6650}  & 6.2 & 3.2 & K1III-IV & $1.123\pm0.015$ & 16.7\\
        \object{HR 7809}  & 6.1 & 3.6 & K1III    & $1.055\pm0.015$ & 31.1\\
        \hline
      \end{tabular}}
      \tablefoot{$m_v$,
  $m_{K{\rm s}}$: magnitudes in $V$ and $K$ bands; UD(K): uniform disk angular
  diameter; $\gamma$: angular distance to~$\eta$~Ser.}
\end{table}