\begin{table}%t1
  \caption{Spectral index $\alpha_{\rm thick}$ results.}
  \label{alphathick}
  %\centering
\small
  \begin{tabular}{c c c c}
    \hline \hline
    Model & $\rm 20^\circ S\ 0^\circ W$ & $\rm 20^\circ S\ 40^\circ W$ & $\rm 20^\circ
    S\ 80^\circ W$ \\
    Low dens. & 1.04 & 1.30 & 1.72 \\
    High dens.& 0.34 & 0.78 & 1.80 \\
    \hline
  \end{tabular}
\end{table}