\begin{table}%t2
  \caption{\label{tab1}Fit results from the baseline model with different $S/N$.}
  \small
  %\centering
\par
  \begin{tabular}{l c c c c}
    \hline\hline
    \noalign{\smallskip}
    Parameter & \multicolumn{3}{c}{Fit result} & Model value\\
    \noalign{\smallskip}
    & $S/N=100$ & $S/N=50$ & $S/N=20$ & \\
      \hline
   \noalign{\smallskip}
   $\theta_{\rm LON}\ \ \ [^{\circ}]\ \ \ \ ({\rm LON\  fit})$             & $-0.9\pm0.8$  & $-1 \pm 1$ & $-5 \pm4$ & $0.00$\\
   $b\ \ \ [\arcsec]\ \ \ \ \ ({\rm LON\  fit})$                               & $-0.001\pm0.002$  & $-0.002\pm 0.003$ & $0.000\pm0.009$ & $0.00$\\
  \noalign{\smallskip}
   $\log_{10}(M_{\rm BH}/M_\odot) $ & $8.05\pm 0.03$ & $8.00\pm 0.06$ & $7.9\pm 0.1$ & $8.00$\\
   $\log_{10}(M/L)\ \ \ [ M_\odot/L_\odot ]\ \ \ \ \ $ & $-9.02$\tablefootmark{a} & $-7.90$\tablefootmark{a} & $0.2\pm2.6$ & $0.00$\\
   $S_0\ \ \ [\arcsec]$                    & $0.02\pm0.02$  & $-0.03 \pm0.03$ & $-0.02 \pm0.03$ & $0.00$\\
   $V_{\rm sys}\ \ \ [{\rm km~s}^{-1}]$                              & $528\pm 26$ & $478 \pm 33$ & $489 \pm 23$ & $500$\\
   $i\ \ \ [^{\circ}]$                                & $35.0$\tablefootmark{b} & $35.0$\tablefootmark{b} & $35.0$\tablefootmark{b} & $35.0$\tablefootmark{b}\\
   $\Delta_{\rm sys}\ \ \ [{\rm km~s}^{-1}]$                             & $25$ & $28$ & $0$ & $-$ \\
   \noalign{\smallskip} 
   reduced $\chi^2 \ \ \ (\chi^2/{\rm d.o.f.})$ & $1.003\ \ (5.12/5)$ & $0.992\ \ (2.976/3)$ & $0.015\ \ (0.031/3)$ & $-$\\
   \noalign{\smallskip}
    $x_{\rm BH}\ \ \ [\arcsec]$                           & $0.02 \pm 0.02$ & $-0.03 \pm 0.03$ & $-0.02 \pm 0.03$ & $0.00$  \\
   $y_{\rm BH}\ \ \ [\arcsec]$                             & $-0.001\pm 0.002$ & $-0.001 \pm 0.004$ & $-0.002 \pm 0.009$ & $0.00$ \\
    \hline
 \end{tabular} 
\tablefoot{\tablefoottext{a}{Parameter not constrained from the fit;}
\tablefoottext{b}{parameter hold fixed.}}
\end{table}