\begin{table}%t6
%\centering
\par
\caption{\label{table:6}C$_{2}$H$_{6}$/(C$_{2}$H$_{6}$+C$_{2}$H$_{2}$) ratios in comets.} 
\begin{tabular}{c c c }       % centered columns (4 columns) 
\hline\hline                 % inserts double horizontal lines 
Comets & C$_{2}$H$_{6}$/(C$_{2}$H$_{6}$+C$_{2}$H$_{2}$) ratios & Remarks \\ 
\hline 
8P/Tuttle        & 0.8~$\pm$~0.2 & This work \\ 
153P/Ikeya-Zhang & 0.8~$\pm$~0.4 & \citet{disanti} \\ 
1P/Halley        & $\sim$0.6   & \citet{disanti} \\ 
C/1996 B2 & 0.8~$\pm$~0.4 & \citet{disanti} \\ 
C/1995 O1 & 0.6~$\pm$~0.2 & \citet{disanti} \\ 
C/1999 H1 & 0.7~$\pm$~0.1 & \citet{disanti} \\ 
C/2001 A2 & 0.8~$\pm$~0.1 & \citet{disanti} \\ 
C/1999 S4 & $>$0.5      & \citet{disanti} \\ 
C/2004 Q2 & 0.9~$\pm$~0.1 & \citet{kobayashi09} \\ 
C/2006 P1 & 0.5~$\pm$~0.1 & \citet{dellorusso09}\\ 
\hline 
\end{tabular} 
\end{table}