\begin{table}%t2
  %\centering
\par
    \caption{Comparison of the spectral slope relative to the $R$ magnitude.\label{tab2}} 
         $$
         \begin{array}{c c c c}
         \hline
         \hline
 {\rm Date}             & m_R & \alpha & \delta \alpha \\
\hline
 {\rm Dec.}/11/1998   & 15.97 & 1.24  & 0.05  \\
\par
 {\rm Mar.}/03/2000   & 15.56 & 1.40  & 0.07  \\
\par
 {\rm Mar.}/04/2000   & 15.60 & 1.38  & 0.02  \\
\par
 {\rm Mar.}/05/2000   & 15.25 & 1.45  & 0.04  \\
\par
 {\rm Nov.}/26/2000   & 16.17 & 1.40  & 0.04  \\
\par
 {\rm Nov.}/28/2000   & 16.32 & 1.30  & 0.04  \\
\par
 {\rm Nov.}/29/2000   & 16.26 & 1.41  & 0.05  \\
\par
 {\rm Dec.}/03/2000   & 16.08 & 1.58  & 0.07  \\
\par
 {\rm Dec.}/04/2000   & 15.89 & 1.55  & 0.05  \\
\par
 {\rm Dec.}/19/2001   & 13.94 & 1.72  & 0.02  \\
\par
 {\rm Apr.}/26/2003   & 15.74 & 1.67  &  0.02  \\
\hline
         \end{array}
    $$
   \end{table}