\begin{table}%t1
%\centering
\par
\caption{\label{tab:err} Estimated Equivalent Width RMS errors
  $\sigma_{EW}$ computed using Eq.~(\ref{eq:sigew}) 
({\it SNR}~=~100 and $N=10^{12}$~cm$^{-2}$).}  
\begin{tabular}{ccccccc}
\hline\hline\noalign{\smallskip}
      &          & \multicolumn{5}{c}{$\delta \lambda$ (\AA\/ pix$^{-1}$)}\\
\cline{3-7}\noalign{\smallskip}
$FWHM$       & $b$          & 0.005& 0.01& 0.02& 0.05& 0.10\\
(km s$^{-1}$)& (km s$^{-1}$) &      &     &     &     &     \\
\hline\noalign{\smallskip}
     & 1.0   &  0.28  &  0.42  &  0.63  &  1.18  &  1.03 \\
3.0  & 3.0   &  0.35  &  0.50  &  0.74  &  1.28  &  1.83 \\
     & 5.0   &  0.45  &  0.65  &  0.95  &  1.69  &  2.42 \\
\cline{2-7}\noalign{\smallskip}
     & 1.0   &  0.37  &  0.52  &  0.77  &  1.43  &  1.86 \\
5.0  & 3.0   &  0.40  &  0.57  &  0.81  &  1.53  &  2.51 \\
     & 5.0   &  0.48  &  0.69  &  1.01  &  1.69  &  2.42 \\
\cline{2-7}\noalign{\smallskip}
     & 1.0   &  0.45  &  0.63  &  0.89  &  1.67  &  2.53 \\
7.0  & 3.0   &  0.46  &  0.66  &  0.93  &  1.75  &  2.51 \\
     & 5.0   &  0.52  &  0.75  &  1.06  &  1.90  &  2.99 \\
\cline{2-7}\noalign{\smallskip}
     & 1.0   &  0.52  &  0.74  &  1.07  &  1.88  &  2.53 \\
9.0  & 3.0   &  0.53  &  0.76  &  1.10  &  1.75  &  3.07 \\
     & 5.0   &  0.58  &  0.83  &  1.17  &  1.90  &  2.99 \\
\hline
\end{tabular}
\tablefoot{Errors are expressed in m\AA.}
\vspace*{-3mm}
\end{table}