\begin{table}%t4
%\centering
\par
\caption{Spectral slopes derived from power-law fitting in the range 1--7~mm 
using literature values (Table~\ref{fluxliterature}) and our \mbox{7-mm} data 
(Col.~2). For objects without centimetre measurements, a 20\% contribution of 
free-free emission was assumed (denoted by brackets in Col.~3). 
Spectral slopes corrected for free-free radiation are listed in 
Col.~4. The estimated dust opacity indices $\beta^{\sim}$ (Col.~5) were corrected for 
optically depth (using $\Delta=0.2$), yielding the final $\beta$ values (Col.~6).}
\label{spectralindex}
\begin{tabular}{lccccc } 
\hline\hline
Source     & \multicolumn{1}{c}{mm slope} & 
             \multicolumn{1}{c}{f--f contribution} &
             \multicolumn{1}{c}{f--f corrected} & 
	     \multicolumn{1}{c}{$\beta$ estimate} &
	     \multicolumn{1}{c}{Opacity index}\\ 
	   & \multicolumn{1}{c}{$\alpha_{\rm mm}$}      &
             \multicolumn{1}{c}{at 7 mm (\%)} &
             \multicolumn{1}{c}{$\alpha_{\rm corr}$} & 
	     \multicolumn{1}{c}{$\beta^{\sim}\!=\!\alpha_{\rm corr}\!-\!2$} &
	     \multicolumn{1}{c}{$\beta=(1+\Delta)\beta^{\sim}$}
\smallskip \\ \hline 
\object{RY Tau}   & 2.51 $\pm$ 0.10  &  24  & 2.66 $\pm$ 0.09  & 0.66 $\pm$ 0.09  & 0.8 $\pm$ 0.1\\
\object{FT Tau}   & 2.62 $\pm$ 0.17  & (20) & 2.76 $\pm$ 0.24  & 0.76 $\pm$ 0.24  & 0.9 $\pm$ 0.3\\
\object{DG Tau B} & 2.88 $\pm$ 0.20  &  24  & 3.17 $\pm$ 0.19  & 1.17 $\pm$ 0.19  & 1.4 $\pm$ 0.2\\
\object{DG Tau}   & 2.45 $\pm$ 0.09  &  20  & 2.54 $\pm$ 0.11  & 0.54 $\pm$ 0.11  & 0.7 $\pm$ 0.1\\
\object{HL Tau}   & 2.93 $\pm$ 0.10  &  23  & 3.04 $\pm$ 0.12  & 1.04 $\pm$ 0.12  & 1.3 $\pm$ 0.1\\
\object{UZ Tau E} & 2.56 $\pm$ 0.08  & (20) & 2.66 $\pm$ 0.09  & 0.66 $\pm$ 0.09  & 0.8 $\pm$ 0.1\\
\object{DL Tau}   & 2.73 $\pm$ 0.11  & (20) & 2.82 $\pm$ 0.14  & 0.82 $\pm$ 0.14  & 1.0 $\pm$ 0.2\\
\object{CI Tau}   & 3.00 $\pm$ 0.27  & (20) & 3.12 $\pm$ 0.30  & 1.12 $\pm$ 0.30  & 1.3 $\pm$ 0.4\\
\object{DO Tau}   & 2.29 $\pm$ 0.06  & (20) & 2.38 $\pm$ 0.07  & 0.38 $\pm$ 0.07  & 0.5 $\pm$ 0.1\\
\object{GM Aur}   & 3.17 $\pm$ 0.20  & (20) & 3.29 $\pm$ 0.20  & 1.29 $\pm$ 0.20  & 1.6 $\pm$ 0.2\\
\hline 
\end{tabular}
\end{table}