\begin{table} %t2
\caption{\label{t:star_stat}Statistics of the field star aperture photometry. For each
  star the mean magnitude and standard deviation are tabulated, along
  with the mean of the individual formal errors, and reference
  magnitude.}
  %\centering
\par
\begin{tabular}{@{}ccccc@{}} 
\hline \hline\noalign{\smallskip}
Star & Mean $R$-mag & $\sigma_{\rm mag} $ & Mean formal error & 
Ref.\ mag \\ 
\noalign{\smallskip}\hline\noalign{\smallskip}
 F  &  13.757  &  0.0033  &  0.0030  &  13.757 \\
 G  &  13.730  &  0.0029  &  0.0029  &  13.730 \\
 H  &  13.977  &  0.0040  &  0.0032  &  13.977 \\
 E  &  14.783  &  0.0048  &  0.0047  &  14.782 \\
 D  &  14.515  &  0.0045  &  0.0041  &  14.515 \\
 X  &  13.422  &  0.0032  &  0.0027  &  13.422 \\
 R  &  16.336  &  0.0135  &  0.0123  &  16.335 \\ 
 \hline
\end{tabular}
\end{table}