OBSERVATIONS OF THE $J=1{\rightarrow}0$ TRANSITIONS OF $^{12}CO,\;^{13}CO\;and\;C^{18}O$ TOWARD OMC-1

Using the Daeduk Radio Telescope, we have observed $J=1\rightarrow0$ transitions of 1$^{12}CO,\;^{13}CO\;and\;C^{18}O$ toward OMC-l. The column densities of $1\~5\times10^{17}\;cm^{-2}\;and\;1\~3\times10^{16}\;cm^{-2}$ have been derived, for $^{13}CO$ and $C^{18}O$, respectively, in the $11'\times11'$ region centered at Orion - KL. The double isotope ratio $[^{13}CO]/[C^{18}O]$ was found to be larger than the cosmic abundance ratio by factors of $2\~10$ which may result from the chemical fractionation effect.