\begin{table}%t1
\caption{\label{params}Relevant parameters of $\alpha$~CMa and its calibrators from the literature.}
%\centerline
{
\begin{tabular}{lcccccc}
\hline\hline
Name & $\alpha$~CMa & $\theta$~Cen & $\delta$~Lep & $\alpha$~Crt & 31~Ori & HR 4050\\
HD number & \object{HD 48915} & \object{HD 123139} & \object{HD 39364} & \object{HD 95272} & 
\object{HD 36167} & \object{HD 89388}\\
\hline
$m_{V}$ & $-$1.47 & 2.06 & 3.80 & 4.07 & 4.71 & 3.38 \\
$m_{K}$ & $-$1.31 & $-$0.10 & 1.31 & 1.62 & 0.90 & 0.60\\
Sp. type & A1V & K0IIIb & G8III/IV & K1III & K5III & K3IIa \\
$ T_{{\rm eff}}$ (K)$^{{a}}$ & 9900  & 4980 & 4580 & 4650 & 3930 & 4500 \\
$[{\rm Fe}/{\rm H}]^{{f}}$ & 0.5 & 0.0 & $-0.75$ &$ -0.$2 & $-0.3$ & 0.5 \\
$\log g ^{{a}}$ & 4.3 & 2.75 & 2.95 & 2.8 & 1.6 & 1.6 \\
$\pi$ (mas)$^{{b}}$ & $379.22 \pm 1.58$ & 53.5 $\pm$ 0.8 & 29.1 $\pm$ 0.6 & 18.7 $\pm$ 1.0 & 7.2 $\pm$ 0.8 & 4.4 $\pm$ 0.5 \\
${\theta_{\rm {LD}}}$ (mas)$^{{c}}$ & ${\bf 6.039 \pm 0.019}^{{g}}$ & $5.434 \pm 0.020^{{e}}$ & 2.63 $\pm$ 0.04 & 2.28 $\pm$ 0.03 & 3.66 $\pm$ 0.06 & 5.23 $\pm$ 0.06 \\
${\theta_{\rm {UD}}}$ (mas)$^{{d}}$ & ${\bf 5.936 \pm 0.016}^{{g}}$ & $5.305 \pm 0.020^{{e}}$ & 2.57 $\pm$ 0.04 & 2.22 $\pm$ 0.03 & 3.55 $\pm$ 0.06 & 5.09 $\pm$ 0.06\\
 \noalign{\smallskip}
\hline
\end{tabular}}
\smallskip
\begin{list}{}{}
\item[$^{{a}}$] From Cohen et~al. (\cite{cohen92}) for $\alpha$~CMa, and from Cayrel de Strobel et~al. (\cite{cayrel}, \cite{cayrel01}) for other stars.
\item[$^{{b}}$] Parallaxes from the {\sc Hipparcos} catalogue (Perryman et~al. \cite{hip}).
\item[$^{{c}}$]  Catalogue values from Cohen et~al. (\cite{cohen99}) for other stars.
\item[$^{{d}}$] Linear limb darkening coefficients factors from Claret et~al.~(\cite{claret95}).
\item[$^{{e}}$] $\theta$~Cen angular diameters from Kervella et~al.~(\cite{kervella03b}).
\item[$^{{f}}$] Qiu et~al. for $\alpha$~CMa, and Cayrel at al. (\cite{cayrel}) for other stars.
\item[$^{{g}}$] Sirius angular diameters from this work (see text for details).
\end{list}
\end{table}