\begin{table}%t9
%%\centering
\par
%\noindent \parbox{15cm}{
\caption{Elemental abundances in NGC~7027, in units
such that $\log N({\rm H})=12.0$. \label{abco}}
%\centerline
{
\begin{tabular}{ccccccccc}
\hline\hline\noalign{\smallskip}
{Element}         &
{This paper}           & {(1)}  &
{(2)}          & {(3)}    &
{(4)}  & {(5)} &{Average$^{{a}}$}  &
Solar$^{{b}}$\\
\hline
 He &11.00 &  11.03 & 11.00 & 11.05 & 11.02 & 11.00   &11.06   & 10.90\\
 C  &9.10  &  8.78  & 8.98  & 8.84  & 9.11  & 8.98    &8.74    &  8.39\\
 N  &8.14  &  8.20  & 8.21  & 8.10  & 8.28  &   &8.35    &  7.83\\
 O  &8.66  &  8.61  & 8.71  & 8.49  & 8.75  & 8.66    &8.68    &  8.69\\
 Ne &8.07  &  8.00  & 8.14  & 8.00  & 8.04  &   &8.09    &  7.87\\
 Mg &7.60  &  7.34  & & 7.41  & 7.33  &   &  &  7.55\\
 S  &6.92  &  6.97  & & 6.86  & 6.90  &   &6.92    &  7.19\\
 Cl &5.21  &  5.04  & & 5.30  & &   &  &  5.26\\
 Ar &6.30  &  6.36  & & 6.32  & 6.40  &   &6.39    &  6.55\\
 Fe &5.58  &  & & & 6.00  &   &  &  7.47\\
\hline\end{tabular}}
\medskip
$^{a}$ Average abundances of Galactic PNe \citep{kingsburgh}.\\
$^{b}$ \citet{lodders}.\\
Reference: { (1) Bernard-Salas et~al. (2001); (2) Kwitter \& Henry (1996);
(3) Keyes et~al. (1990); (4) Middlemass (1990); (5)~Gruenwald \&
P{\' e}quignot (1989).}
\end{table}