\begin{table}%t1
\caption{\label{logbook1}Logbook of the photometric observations of HD~180~642. }
%\centerline
 {
\begin{tabular}{llrllll} \hline  \hline
Observatory & $N$ & $\Delta T$ & HJD begin & HJD end & Filter(s) &$f_1$ \\
\hline
La Silla & 20 & 186.7 & 50~562.8 & 50749.6 & UB$_1$BB$_2$V$_1$VG & 5.4870(2) \\
La Palma & 171 & 11~83.8 & 52~421.6 & 53605.4 & UB$_1$BB$_2$V$_1$VG & 5.48693(1) \\
SPMO & 113 & 5.3 & 53~192.7 & 53~198.0 & $u,v,b,y$ & 5.494(3) \\
SNO & 222 & 359.2 & 53~205.4 &  53~564.6 & $u,v,b,y$ & 5.48693(3)\\
KO  & 84 & 319.2 & 53~260.3 & 53~579.5 & Johnson $V$ & 5.49(1)\\ 
KO CCD & 261 & 26.1 & 53~921.4 & 53~947.5 & Johnson $V$ & 5.4858(3)\\
ASAS & 363 & 2797.6 & 51~979.9 & 54~777.5 & Johnson $V$ & 5.486915(7)\\
\hline
Str\"omgren & 335 & 371.9 &  53~192.7 & 53564.6 & $u,v,b,y$ & 5.48693(2) \\
U & 526 & 3042.6 & 50~562.8 & 53~605.4 & U, $u$ & 5.48695(2) \\
B & 526 & 3042.6 & 50~562.8 & 53~605.4 & B, $v$ & 5.486947(2) \\
V & 526 & 3042.6 & 50~562.8 & 53~605.4 & V, $y$ & 5.486944(2) \\
V+ & 1234 & 4214.7 & 50~562.8  & 54~777.5 & V, $y$, $V$ & 5.486938(5) \\
\hline
\end{tabular}}
\par
\smallskip
 {The number $N$ of datapoints retained for the analysis, the total timespan $\Delta T$ (in days) and the available filters are given. The last column gives the value of the dominant frequency (see Sect.~\ref{freqsection}) expressed in d$^{-1}$ with its error between brackets. The HJD is given with respect to ${\it HJD}_0= 2~400~000$. Str\"omgren refers to merged SPMO and SNO Str\"omgren data. The merged Geneva U and Str\"omgren~$u$, B and $v$, and V and $y$~data, are denoted as 
 U, B, V~data, respectively. The V+ dataset corresponds to the $V$~data to which the KO Johnson $V$ data and ASAS Johnson $V$~data are also added.} 
\end{table}