\begin{table}%t2
\caption {\label{tab_beta_med}Median values of the emissivity spectral index ($\rm \beta$) in the
molecular and the atomic phase for each studied case and each
wavelength.   }
%\centerline
 {\begin{tabular}{ c   c  c   c  c   c   c }
\hline
\hline
$\rm \lambda$ &  \multicolumn{2}{c }{Case 1: \CaseOne} &  \multicolumn{2}{c }{ Case 2: \CaseTwo} &   \multicolumn{2}{c }{Case 3: \CaseThree} \\
 ($\rm \mic$)& $\rm \beta_{HI}$ & $\rm \beta_{CO}$ & $\rm \beta_{HI}$ & $\rm \beta_{CO}$ & $\rm \beta_{HI}$ & $\rm \beta_{CO}$ \\
\hline
 100 & 2.3 $\pm$ 1.7 & 3.0 $\pm$ 2.3 & 1.7 $\pm$ 1.9 & 2.9 $\pm$ 2.1 & 2.1 $\pm$ 3.3 & 2.0 $\pm$ 1.7\\
 140 & 2.4 $\pm$ 0.5 & 2.5 $\pm$ 0.6 & 2.1 $\pm$ 0.6 & 2.8 $\pm$ 0.6 & 2.8 $\pm$ 0.9 & 2.1 $\pm$ 0.5 \\
 240 & 2.3 $\pm$ 0.3 & 2.5 $\pm$ 0.3 & 1.8 $\pm$ 0.2  & 2.7 $\pm$ 0.3 & 2.3 $\pm$ 0.3 & 1.9 $\pm$ 0.2 \\
 550 & 1.9 $\pm$ 0.3 & 2.1 $\pm$ 0.2 & 1.5 $\pm$ 0.2 & 2.3 $\pm$ 0.2 & 2.0 $\pm$ 0.3 & 2.0 $\pm$ 0.3 \\
 850 & 1.6 $\pm$ 0.3 & 1.3 $\pm$ 0.2 & 1.5 $\pm$ 0.2 & 1.5 $\pm$ 0.2 & 1.7 $\pm$ 0.2  & 1.6 $\pm$ 0.2  \\
 1400 & 1.5 $\pm$ 0.4 &  1.3 $\pm$ 0.2 & 1.6 $\pm$ 0.3 & 1.5 $\pm$ 0.3 & 1.3 $\pm$ 0.2 & 1.5 $\pm$ 0.3 \\
 2100 & 1.2 $\pm$ 0.2 & 1.3 $\pm$ 0.2 & 1.7 $\pm$ 0.3 & 1.6 $\pm$ 0.3 & 1.3 $\pm$ 0.3 & 1.7 $\pm$ 0.3  \\
 3200 & 1.2 $\pm$ 0.6 & 0.8 $\pm$ 0.5 & 2.1 $\pm$ 0.7  & 1.3 $\pm$ 0.8 & 2.2 $\pm$ 0.6  & 1.4 $\pm$ 0.8 \\
\hline
\end{tabular}}
\smallskip
Error bars represent the 1-$\rm \sigma$ uncertainty
estimates.
\par
\end{table}