\begin{table}%t3
\caption{Ammonia line observations of comets at MPIfR and
upper limits on the NH$_3$ column density.
% [COLUMN 6 WAS RECALCULATED; FOOTNOTES WERE REARRANGED;
% $\Delta v$ IS NOW $\delta v$;
% COMET P/153: COLUMN 5 WAS RECALCULATED AND
% $\delta v$ = 1.9 IS NOW $\delta v = 1.7$.]
\label{obs_table}}
%\centerline
{\begin{tabular}{cccccccc}
\hline\hline
Line & Frequency &
$T_{\rm rms}$ &
$T_{99.7\%}$ &
%$[ \int T_{\scriptscriptstyle{MB}} \; dv ]_{\rm max}^{\; b}$ &
$[ \int T_{\scriptscriptstyle{\rm MB}} \; {\rm d}v ]_{\rm max}~$ $^a$ &
$\langle N(J,J) \rangle_{\rm max}~$ $^b$  
&$n(J,J)$ $^c$
&$\langle N(\hbox{NH}_3) \rangle_{\rm max}$
\\
(J,J)    & &  [mK] &  [mK] 
& [mK~km s$^{-1}$]
& [10$^{12}$~cm$^{-2}$]
&  
& [10$^{12}$~cm$^{-2}$]
\\ 
\hline
%  & & &  & & &&\\[-3mm]
\multicolumn{6}{l}{Comet C/2001 A2-B (LINEAR):
7 Jul. 2001 ($\Delta t$~= 70 min, $\delta v = 1.4\hbox{ km s}^{-1}$)}  \\
(1,~1) & 23.69450 &   16 & 36 & 54 & 0.73 &0.26 &$<$$2.8$\\
(2,~2) & 23.72263 &   16 & 30 & 45 & 0.46 &0.18 &$<$$2.5$\\
(3,~3) & 23.87013 &   16 & 34 & 51 & 0.46 &0.20 &$<$$2.3$\\
(4,~4) & 24.13942 &   15 & 30 & 45 & 0.38 &0.05 &$<$$7.6$\\
\multicolumn{6}{l}{Lowest upper bound $^d$} &     &\boldmath$<$$2.3$ \\
%  & & &  & & &&\\[-3mm]
\multicolumn{6}{l}{Comet 153P/Ikeya-Zhang:
% 25 Apr., 4, 6, 7 May 2002 ($\Delta t$~= 53 min, $\delta v = 1.8\hbox{ km s}^{-1}$)}  \\
% (1,1) & 23.69450 &   12 & 30 %40 & 57 & 0.85 &0.26 & $<3.0$\\
% (2,2) & 23.72263 &   15 & 28 %26 & 54 & 0.47 &0.18 & $<3.0$\\
% (3,3) & 23.87013 &   16 & 40 %40 & 77 & 0.61 &0.20 & $<3.5$\\
% (4,4) & 24.13942 &   14 & 16 %14 & 34 & 0.15 &0.05 & $<5.9$\\
% Total &          &      &    &    &      &     &\boldmath$<3.0$ $^d$\\
25 Apr. 2002 $^e$  ($\Delta t$~= 53 min, $\delta v = 1.8\hbox{ km s}^{-1}$)}  \\
(1,~1) & 23.69450 &   12 & 40  & 77 & 1.04 &0.26 & $<$$4.0$\\%40
(2,~2) & 23.72263 &   15 & 26  & 50 & 0.51 &0.18 & $<$$2.8$\\%26
(3,~3) & 23.87013 &   16 & 40  & 77 & 0.69 &0.20 & $<$$3.5$\\%40
(4,~4) & 24.13942 &   14 & 14  & 27 & 0.23 &0.05 & $<$$4.6$\\%14
\multicolumn{6}{l}{Lowest upper bound $^d$} &     &\boldmath$<$$2.8$ \\
 % & & &  & & &&\\[-3mm]                       
\multicolumn{6}{l}{Comet C/2001 Q4 (NEAT):
8,~13,~17 May 2004 ($\Delta t$~= 219 min, $\delta v = 1.7\hbox{ km s}^{-1}$)}  \\
(1,~1) & 23.69450 &  18 & 20 & 36 & 0.49 &0.26 & $<$$1.9 $\\
(2,~2) & 23.72263 &  19 & 28 & 51 & 0.52 &0.18 & $<$$2.9 $\\
(3,~3) & 23.87013 &  19 & 44 & 80 & 0.72 &0.20 & $<$$3.6 $\\
(4,~4) & 24.13942 &  23 & 20 & 36 & 0.31 &0.05 & $<$$6.2$\\
\multicolumn{6}{l}{Lowest upper bound $^d$} &     &\boldmath$<$$1.9$ \\
 % & & &  & & &&\\[-3mm]
\multicolumn{6}{l}{Comet C/2002 T7 (LINEAR): 
8,~13 May 2004 ($\Delta t$~= 98 min, $\delta v = 1.9\hbox{ km s}^{-1}$)}  \\
(1,~1) & 23.69450 &  29 & 30  & 61 & 0.82 &0.26 & $<$$3.2 $\\
(2,~2) & 23.72263 &  29 & 82  & 166 & 1.69 &0.18 & $<$$9.4 $\\
(3,~3) & 23.87013 &  29 & 52  & 105 & 0.95 &0.20 & $<$$4.8 $\\
(4,~4) & 24.13942 &  47 & 80  & 162 & 1.37 &0.05 & $<$$27.4$\\
\multicolumn{6}{l}{Lowest upper bound $^d$} &     &\boldmath$<$$3.2$ \\
\hline
\end{tabular}}
\par
\smallskip
$^a$ {$1.064 \cdot T_{99.7\%} \cdot \delta v$ with $\delta v$ values as given in the table.}\\
$^b$ {From Eq.~(\ref{NJJ}).}\\
$^c$ {Defined in Eq.~(\ref{njj}).}\\
$^d$ {Lowest upper limit on $\langle N(\hbox{NH}_3) \rangle$
from the four lines observed.}\\
$^e$ {Calculations based on the best single epoch of
observations.}
\end{table}