\begin{table}%t3
\caption{\label{table:3} The abundance ratio of CCH and its $^{13}$C isotopic species.}             
%\centering
\par
\begin{tabular}{ccc}        
\hline\hline  
\noalign{\smallskip}              
Ratio&TMC-1&L1527  \\     
\hline  \noalign{\smallskip}                  
\multicolumn{1}{c}{[CCH]/[C$^{13}$CH]\tablefootmark{a}}&$\geq$170&$\geq$80  \\   % inserting body of the table
\multicolumn{1}{c}{[CCH]/[$^{13}$CCH]\tablefootmark{b}}&$\geq$250&$\geq$135  \\   
\multicolumn{1}{c}{[C$^{13}$CH]/[$^{13}$CCH]$^{b}$}&1.6(4)&1.6(1) \\ 
\hline
\end{tabular}
\tablefoot{The numbers in parentheses represent the three sigma errors in units of the last significant digits.
\tablefoottext{a}{Derived from the LVG model.  [$X$] represents the abundance of $X$, and the [$X$]/[$Y$] ratio can be obtained from the column densities of $X$ and $Y$, assuming that both molecules exist in the same region.}
\tablefoottext{b}{Derived from the integrated intensity ratio of the strongest hyperfine components of C$^{13}$CH and $^{13}$CCH.}}
\end{table}