\begin{table}%t7
 \caption{Physical properties of ejecta.}\label{tab7}
%\centerline
{
 \begin{tabular}{crrrrrcc}
 \hline   \hline
 Date  & April 26 & May 15 & June 9 & Sep. 9 & Sep. 16 & mean & unit \\
 days  & 144.7 & 163.7 & 188.7 & 281.4 & 288.5 & & \\ \hline
 $T_{\rm e}$ & 10~600 & 10~700 & 10~700 & 10~900 & 10~600 & 10~700 $\pm$ $100$ & K \\
 $N_{\rm e}$ & 9.4 & 8.7 & 7.8 & 5.8 & 5.2 & & 10$^6$ cm$^{-3}$ \\
 He I 5876 C/R &  0.25 & 0.26 & 0.26 & 0.28 & 0.25 & & \\
 $N({\rm He^+})/N({\rm H})$ & 0.10 & 0.09 & 0.09 & 0.05 & 0.05 & & \\
 $N({\rm He^{++}})/N({\rm H})$ & 0.04 & 0.04 & 0.07 & 0.08 & 0.07 & & \\
 $N({\rm He})/N({\rm H})$  & 0.14 & 0.13 & 0.16 & 0.13 & 0.12 & $0.13$ $\pm$ $0.01$ & \\
 $m$(H) & 4.7 & 4.6 & 4.7 & 1.5 & 1.0 & $4.7$ $\pm$ $1.0$ & $10^{-5}~M_{\odot}$ \\
 $m$(total)  & 6.2 & 6.0 & 6.3 & 1.9 & 1.3 & $6.2$ $\pm$ $1.4$ & $10^{-5}~M_{\odot}$ \\
\hline
 \end{tabular}}
\medskip 
 The means of $m$(H) and $m$(total) are those of April, May and June.
\end{table}