\begin{table}%t6 \caption{\label{spectral_indices_opt}Optical spectral indices and classifications for \epsba,~Bb.} \small%\centerline { \begin{tabular}{lll} \hline \hline\noalign{\smallskip} Index & $\varepsilon$~Indi~Ba & $\varepsilon$~Indi~Bb\\ \hline \ion{Cs}{i}(A) & 2.147 (T2.0 $\pm$ 1.0) & 1.738 (T6.0 $\pm$ 1.0) \\ CrH(A) / H$_{2}$O & 0.906 (T0.0 $\pm$ 1.0) & 0.452 (T6.0 $\pm$ 1.0) \\ FeH(B) & 1.237 ($<$T4?) & 1.109 (T6.5 $\pm$ 0.5) \\ Colour-e & 3.323 (T0.0 $\pm$ 1.0) & 4.135 ($>$T2) \\ \hline Mean & T0.5 & T6.0 \\ Direct & $<$T2.0 & T6.0 \\ \hline \end{tabular}} \medskip The spectra have not been smoothed to derive these indices. Direct classification compares the overall spectral shape with the standard star spectra. The spectral type derived from each index is shown in parentheses after each measurement. The spectral range of the FeH(B)~index is limited to types later than~T2 and the range of the colour-e~index to types earlier than~T2. The approximate classification from direct comparison for Ba is due to the lack of a~T0 or T1~optical spectral standard. \end{table}