\begin{table}%t1
%\centering
\par
\caption{\label{tbl:obs}Four Stokes parameter
spectropolarimetric observations of \cvn\ used for Magnetic Doppler Imaging.} 
\begin{tabular}{lcccrrrcccc}
\hline\hline
\noalign{\smallskip}
UT Date & \multicolumn{3}{c}{Stokes}     & \multicolumn{3}{c}{JD (2~450~000+)} & & & $S/N$\\
        & \multicolumn{3}{c}{Parameters} & $Q$~~~~~ & $U$~~~~~ & $V$~~~~~ & $\overline{\varphi}$ &  $\delta\varphi$ & range\\
%\noalign{\smallskip}
\hline
%\noalign{\smallskip}
 18 Feb. 1997   &  $Q$ & $U$ & $V$ &  498.511 &  498.531 &  498.489 & 0.038 & 0.004 & 420--550 \\
 19 Feb. 1997   &  $Q$ & $U$ & $V$ &  499.532 &  499.555 &  499.511 & 0.225 & 0.004 & 650--690 \\
 20 Feb. 1997\tablefootmark{a}   &      &     & $V$ &          &          &  500.422 & 0.387 &       & 550      \\
 21 Feb. 1997   &  $Q$ & $U$ & $V$ &  501.490 &  501.504 &  501.470 & 0.582 & 0.003 & 270--320 \\
 22 Feb. 1997   &  $Q$ &     & $V$ &  502.549 &          &  502.519 & 0.773 & 0.003 & 320--490 \\
 23 Feb. 1997   &  $Q$ & $U$ & $V$ &  503.497 &  503.516 &  503.474 & 0.949 & 0.004 & 240--280 \\
 25 Feb. 1997\tablefootmark{b} &      &     & $V$ &          &          &  505.581 & 0.331 &       & 470      \\
 25 Feb. 1997   &  $Q$ & $U$ &     &  505.695 &  505.715 &          & 0.353 & 0.002 & 410--410 \\
 07 Feb. 1998   &  $Q$ & $U$ & $V$ &  852.562 &  852.584 &  852.539 & 0.771 & 0.004 & 740--890 \\
 09 Feb. 1998   &  $Q$ & $U$ & $V$ &  854.561 &  854.584 &  854.539 & 0.137 & 0.004 & 820--1020 \\
 11 Feb. 1998   &  $Q$ & $U$ & $V$ &  856.545 &  856.567 &  856.524 & 0.499 & 0.004 & 910--1020 \\
 12 Feb. 1998   &  $Q$ & $U$ & $V$ &  857.675 &  857.694 &  857.657 & 0.706 & 0.003 & 820--880 \\
 13 Feb. 1998   &  $Q$ & $U$ & $V$ &  858.555 &  858.574 &  858.537 & 0.867 & 0.003 & 710--810 \\
 15 Feb. 1998   &  $Q$ & $U$ & $V$ &  860.605 &  860.626 &  860.586 & 0.242 & 0.004 & 500--720 \\
 16 Feb. 1998   &  $Q$ & $U$ & $V$ &  861.606 &  861.627 &  861.584 & 0.424 & 0.004 & 560--750 \\
 17 Feb. 1998   &  $Q$ & $U$ & $V$ &  862.533 &  862.554 &  862.515 & 0.594 & 0.004 & 560--560 \\
 19 Feb. 1998   &  $Q$ & $U$ & $V$ &  864.603 &  864.638 &  864.576 & 0.973 & 0.006 & 430--590 \\
 15 Jan. 1999   &  $Q$ &     & $V$ & 1194.621 &          & 1194.600 & 0.310 & 0.002 & 400--450 \\
 19 Jan. 1999   &  $Q$ & $U$ & $V$ & 1198.652 & 1198.672 & 1198.633 & 0.049 & 0.004 & 770--840 \\
 26 Jul. 2004   &  $Q$ & $U$ & $V$ & 3213.362 & 3213.381 & 3213.400 & 0.413 & 0.004 & 440--480 \\
\hline
\end{tabular}
\tablefoot{Columns give the UT date for the beginning of the night when observation was obtained, the Stokes parameters observed (in addition to Stokes~$I$), the Julian Dates of mid-exposure
for each observed Stokes parameter, the mean phase $\overline{\varphi}$ for all observed Stokes 
parameters, the maximum difference $\delta\varphi$ between $\overline{\varphi}$  and the phases of 
individual Stokes parameter observations, the range of the signal-to-noise
ratio per 2.6~km~s$^{-1}$ spectral pixel for two or three exposures.\\
\tablefoottext{a}{The Stokes~$Q$ and $U$ spectra are disregarded. See text for detailed explanation.}
\tablefoottext{b}{The Stokes~$V$ observation is considered individually due to a larger-than-average phase difference with respect to the linear polarization spectra obtained on that night.}}
\end{table}