\begin{table}%t1
%\centering
\par
\caption{Spin period of RBS1223 at given epoch with given instrument. All
  periods listed are newly derived values. 
\label{t:spin}} 
\begin{tabular}{lll}
\hline\hline
  Epoch MJD & Period & Instrument\\
(days)  &       (s)  &      \\
\hline
50~824.21390  &   $\rm 10.31227_{-0.00011}^{+0.00012}$ &  Rosat HRI\\
51~719.51835  &   $\rm 10.31307_{-0.00048}^{+0.00060}$ &  Chandra ACIS-S\\
52~274.25598  &   $\rm 10.31253_{-0.00029}^{+0.00030}$ &  XMM PN AO1\\
52~640.43264  &   $\rm 10.31250_{-0.00020}^{+0.00020}$ &  XMM PN CAL1\\
53~003.46683  &   $\rm 10.31258_{-0.00018}^{+0.00018}$ &  XMM PN CAL2\\
53~095.33034  &   $\rm 10.31250_{-0.00012}^{+0.00004}$ &  Chandra LETGS\\
\hline
\end{tabular}
\end{table}