\begin{table}%T2
\caption{Period determinations.}\label{t2}
%\centerline
 {\small
\begin{tabular}{l cc c}
%\noalign{\smallskip\smallskip}
\hline\hline\\[-2.8mm]
%\noalign{\smallskip\smallskip}
\hfil Method \hfil &
\multispan{2}{\hfil $P_{\rm rot}$ \hfil} &
\hfil Reference \hfil \\[-1.2mm]
 & \multicolumn{2}{@{\hspace*{-0.01cm}}c}{\rule[0.5ex]{2.0cm}{0.3pt}} & \\[-1.2mm]
 & \hfil (day) \hfil &
   \hfil (hour) \hfil & \\
%\noalign{\smallskip\smallskip}
\hline
%\noalign{\smallskip\smallskip}
Autocorrel. MAC & 0.536 & 12.86 & B+78 \\
Inform. entropy & 0.529 & 12.69 & C+95 \\
DFT             & 0.491 & 11.78 & K75, D85 \\
Lomb-Scargle    & 0.418 & 12.44 & L76, S82 \\
PDM             & 0.417 & 12.42 & S78 \\
AoV             & 0.525 & 12.61 & S89, S91 \\
WindowCLEAN     & 0.503 & 12.07 & BG88 \\ 
%\noalign{\smallskip\smallskip}
\hline
%\noalign{\medskip}
Mean            & 0.517 & 12.41 & \\
%\noalign{\smallskip}
$1\sigma$ error & 0.017 & 0.41 & \\
%\noalign{\medskip}
\hline
\end{tabular}}
\par
\medskip
Note:\\
B+78: Burki et~al. (\cite{Burki78}).\\
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BG88: Belton \& Gandhi (\cite{Belton88}).\\
%\noalign{\smallskip}
C+95: Cincotta et~al. (\cite{Cincotta95}).\\
%\noalign{\smallskip}
K75: Kurtz (1975).\\
%\noalign{\smallskip}
D+85: Deeming (1985).\\
%\noalign{\smallskip}
L76: Lomb (\cite{Lomb76}).\\
%\noalign{\smallskip}
S82: Scargle (\cite{Scargle82}).\\
%\noalign{\smallskip}
S78: Stellingwerf (\cite{Stellingwerf78}).\\
%\noalign{\smallskip}
S89, S91: Schwarzenberg-Czerny (\cite{Schwarzenberg89}, \cite{Schwarzenberg91}).
\end{table}