\begin{table}%T3 \caption{\label{colorcor}Photometric colour corrections.} \small %\centering \par \begin{tabular}{lcccccc} \hline \hline \noalign{\smallskip} BB temp. & CC\_70 & CC\_100 & CC\_160 \\ \hline BB (10~000 K) & 1.02 & 1.03 & 1.07 \\ BB (5000 K) & 1.02 & 1.03 & 1.07 \\ BB (1000 K) & 1.01 & 1.03 & 1.07 \\ BB (500 K) & 1.01 & 1.03 & 1.07 \\ BB (250 K) & 1.01 & 1.02 & 1.06 \\ BB (100 K) & 0.99 & 1.01 & 1.04 \\ BB (50 K) & 0.98 & 0.99 & 1.01 \\ BB (20 K)\tablefootmark{a} & 1.22 & 1.04 & 0.96 \\ BB (15 K) & 1.61 & 1.16 & 0.99 \\ BB (10 K) & 3.65 & 1.71 & 1.18 \\ \hline \noalign{\smallskip} Power law ($\nu^{\beta}$) & CC\_70 & CC\_100 & CC\_160 \\ \hline $\beta = -3.0 $ & 1.04 & 1.04 & 1.06 \\ $\beta = -2.0 $ & 1.02 & 1.01 & 1.02 \\ $\beta = -1.0 $ & 1.00 & 1.00 & 1.00 \\ $\beta = 0.0 $ & 1.00 & 1.00 & 1.00 \\ $\beta = 1.0 $ & 1.00 & 1.01 & 1.03 \\ $\beta = 2.0 $ & 1.02 & 1.03 & 1.08 \\ $\beta = 3.0 $ & 1.04 & 1.07 & 1.14 \\ \hline \end{tabular}\tablefoot{\tablefoottext{a}{Colour corrections for sources with temperatures below 20~K can become quite significant, in particular at 70~$\mu$m.\\ Photometric reference spectrum: $\nu F_{\nu}=\lambda F_{\lambda}=\rm{const.}$. PACS bolometer reference wavelengths: {70.0, 100.0, 160.0~$\mu$m}. In order to obtain a monochromatic flux density one has to divide the measured and calibrated band flux by the above tabulated values. } } \end{table}