\begin{table}%t1
 %\centering
\par
 \caption{\label{tab:abund}Chemical composition of HD~170987 measured relative to the Sun ($\Delta A$). $n$ is the number of spectral lines used.}
\begin{tabular}{l|lr|lllr}
\hline
\hline
El.            & $\Delta A $ (dex)            & $n$  & El.             & $\Delta A$   (dex)         & $n$ \\
\hline
\par
  {Li \sc   i} &     $  1.80       $   &   1  &    {Ca \sc   i} &     $ -0.10~\pm~0.03$   &  11  \\ 
  {C  \sc   i} &     $ -0.27       $   &   2  &    {Sc \sc  ii} &     $ -0.16~\pm~0.06$   &   3  \\ 
  {O  \sc   i} &     $ -0.02       $   &   1  &    {Ti \sc   i} &     $ -0.15~\pm~0.05$   &   4  \\ 
  {Na \sc   i} &     $ -0.18       $   &   2  &    {Ti \sc  ii} &     $ -0.15~\pm~0.08$   &   2  \\ 
  {Mg \sc   i} &     $ -0.25       $   &   1  &    {Cr \sc   i} &     $ -0.18~\pm~0.05$   &   7  \\ 
  {Mg \sc  ii} &     $ -0.22       $   &   1  &    {Cr \sc  ii} &     $ -0.17~\pm~0.05$   &   5  \\ 
  {Al \sc   i} &     $ -0.22~\pm~0.10$   &   4  &    {Fe \sc   i} &     $ -0.15~\pm~0.03$   & 143  \\ 
  {Si \sc   i} &     $ -0.19~\pm~0.03$   &  11  &    {Fe \sc  ii} &     $ -0.15~\pm~0.03$   &  20  \\ 
  {Si \sc  ii} &     $ -0.16~\pm~0.03$   &   2  &    {Ni \sc   i} &     $ -0.27~\pm~0.03$   &  16  \\ 
  {S  \sc   i} &     $ -0.27       $   &   2  &    {Y  \sc  ii} &     $ -0.10       $   &   1  \\ 
  \hline
\end{tabular}
\end{table}