\begin{table}%t1
\caption{The authors from which we adopt the observational data for each considered element.}
 \label{authors}
%\centering
\small
\begin{tabular}{cccccccccc}
\hline\hline
                    & Eu& Ba& La& Sr& Y & Zr& Ca& Mg& Si\\
\hline
Burris et~al. (\cite{Burr00})              & X & X &   & X & X & X &   &   &   \\
Carney et~al. (\cite{Carne97})              &   &   &   &   &   &   & X & X & X \\
Carretta et~al. (\cite{Carre02})            &   &   &   &   &   &   & X & X & X \\
Cayrel  et~al. (\cite{Cayr04})             &   &   &   &   &   &   & X & X & X \\
Cowan et~al. (\cite{Cowa05})               & X &   & X &   &   & X &   &   &   \\
Edvardsson et~al. (\cite{Edva93})          &   & X &   &   & X & X & X & X & X \\
Fran\c cois et~al. (\cite{Franc07})         & X & X & X & X & X & X &   &   &   \\
Fulbright (\cite{Fulb00})                  & X & X &   &   & X & X & X & X & X \\
Fulbright (\cite{Fulb02})		  & X & X &   &   & X & X & X & X & X \\	Gilroy et~al. (1998)		  & X & X & X & X & X & X &   &   &   \\
Gratton \& Sneden (\cite{Grat88})	  &   & X &   & X & X &   &   &   &   \\
Gratton \& Sneden (\cite{Grat94})	  & X & X & X & X & X & X &   &   &   \\
Honda et~al. (\cite{Hond04}) 		  & X & X & X & X & X & X & X & X & X \\
Ishimaru et~al. (\cite{Ishim04})		  & X & X &   & X &   &   &   &   &   \\
Johnson (\cite{Johns02})                    & X & X & X & X & X & X & X & X & X \\
Koch \& Edvardsson (\cite{Koch02})	  & X &   &   &   &   &   &   &   &   \\
Mashonkina \& Gehren (\cite{Masho00}, \cite{Masho01}) & X & X &   & X &   &   &   &   &   \\
McWilliam et~al. (\cite{McWi95})		  & X & X & X & X & X & X & X & X & X \\
McWilliam \& Rich (\cite{McWi94})	  & X & X & X &   & X & X & X & X & X \\
Nissen \& Schuster (\cite{Niss97})         &   & X &   &   & X &   &   &   &   \\
Pompeia et~al. (\cite{Pompe03})		  &   &   & X &   &   &   &   &   &   \\
Prochaska et~al. (\cite{Proc00})		  & X & X &   &   & X &   & X & X & X \\
Ryan et~al. (\cite{Ryan91})		  & X & X &   & X & X &   & X & X & X \\
Ryan et~al. (\cite{Ryan96})		  & X & X &   & X & X & X & X & X & X \\
Stephens (\cite{Step99})  		  &   & X &   &   & X &   & X & X & X \\
Stephens \& Boesgaard (\cite{Step02})      &   & X &   &   & X &   & X & X & X \\
\hline
\end{tabular}
\end{table}