\begin{table}%t1
\par
\caption{\label{obs}List of optical, near-IR, and radio observatories contributing data to this work.}
%\centerline
 {
\begin{tabular}{l r c  }
\hline\hline
Observatory    & Tel.\ size    & Bands\\%               & $N_{\rm obs}$\\
\hline
\multicolumn{3}{c}{\it Optical}\\
Abastumani, Georgia      &  70 cm         & $R$                \\%Long=+34.0125 deg, Lat=+44.7266 deg, Alt=650 m
ARIES, India             & 104 cm         & $BVRI$             \\
Armenzano, Italy         &  35 cm         & $BRI$              \\
Armenzano, Italy         &  40 cm         & $BVRI$             \\
Belogradchik, Bulgaria   &  60 cm         & $VRI$              \\
BOOTES-2, Spain          &  30 cm         & $R$                \\
Bordeaux, France         &  20 cm         & $V$                \\
Calar Alto, Spain$^a$    & 220 cm         & $R$                \\
Crimean, Ukraine         &  70 cm         & $BVRI$             \\
Kitt Peak (MDM), USA     & 130 cm         & $UBVRI$            \\
L'Ampolla, Spain         &  36 cm         & $R$                \\%Long=+0.670136 deg, Lat=+40.807 deg, Alt=75 m
Lulin (SLT), Taiwan      &  40 cm        & $R$                \\
Michael Adrian, Germany  & 120 cm        & $R$                \\%Long=+8.4114 deg, Lat=+49.9254, Alt=103 m
Mt.\ Lemmon, USA         & 100 cm        & $BVRI$             \\
New Mexico Skies, USA    &  30 cm        & $VRI$              \\
Roque (KVA), Spain       &  35 cm        & $R$                \\
Roque (NOT), Spain       & 256 cm        & $UBVRI$            \\
Rozhen, Bulgaria         & 50/70 cm      & $BVR$              \\%Long=+24.7439 deg, Lat=+41.6931, Alt=1759 m
Rozhen, Bulgaria         & 200 cm        & $BVRI$             \\%Long=+24.7439 deg, Lat=+41.6931, Alt=1759 m
Sabadell, Spain          &  50 cm        & $R$                \\
San Pedro Martir, Mexico &  84 cm        & $R$                \\
Sobaeksan, South Korea   &  61 cm        & $VRI$              \\  
Sommers-Bausch, USA      &  61 cm        & $VRI$              \\
St.\ Petersburg, Russia  &  40 cm        & $BVRI$             \\
Talmassons, Italy        &  35 cm        & $BVR$              \\
Teide (BRT), Spain       &  35 cm        & $BVR$              \\
Torino, Italy            & 105 cm        & $BVRI$             \\
Tuorla, Finland          & 103 cm        & $R$                \\
Univ.\ of Victoria, Canada & 50 cm       & $R$                \\
Valle d'Aosta, Italy     &  81 cm        & $BVRI$             \\%Long=+7.47833 deg, Lat=+45.7895 deg, Alt=1600 m
\hline
\multicolumn{3}{c}{\it Near-infrared}\\
Campo Imperatore, Italy  & 110 cm        & $JHK$          \\
Roque (NOT), Spain       & 256 cm        & $HK$          \\
\hline
\multicolumn{3}{c}{\it Radio}\\
Crimean (RT-22), Ukraine & 22 m          & 37 GHz          \\%lat=+44:23:52.6, long=2h 15m 55.1s
Mauna Kea (SMA), USA     &$8 \times 6$ m$^b$ & 230, 345 GHz      \\
Medicina, Italy          & 32 m          & 5, 8, 22 GHz        \\
Mets\"ahovi, Finland     & 14 m          & 37 GHz              \\
Noto, Italy              & 32 m          & 43 GHz              \\
UMRAO, USA               & 26 m          & 4.8, 8.0, 14.5 GHz   \\
\hline\end{tabular}}
\par
\smallskip
 {$^a$ Calar Alto data were acquired as part of the MAPCAT (Monitoring}\\
 {AGN with Polarimetry at the Calar Alto Telescopes) project.}\\
 {$^b$ Radio interferometer including 8 dishes of 6 m size.}
\end{table}