\begin{table}%t2
%\centering
\par
\caption{Non-gravitational parameters in units of $10^{-8}$ AU/day$^2$ for
46P/Wirtanen.\label{tab2}}
{
\begin{tabular}{llccccc}\hline\hline
Source & Obs. interval & No. of obs. & $A_1$ & $A_2$ & $A_3$ & rms\\ 
\\\hline
Marsden (1983) & 1948--1975 & 36 & +0.52 & $-$0.0871 & -- & $1''$86 \\
Krolikowska & 1948--1975 & 45 & +0.5735 & $-$0.0872 & +0.2019 & $1''$90 \\
\& Sitarski (1996) \\
Grav (2001) & 1948--1975 & 45 & +0.6969 & $-$0.0877 & +0.1712 & $1''$87 \\
Grav (2001) & 1986--1999 & 338 & +0.5029 & $-$0.1690 & $-$0.0097 & $1''$27 \\
Grav (2001) & 1960--1999 & 360 & +0.7218 & $-$0.1661 & $-$0.1866 & $3''$15 \\
\hline 
\end{tabular}} 
\end{table}