Detection of (CO)-C-13-O-17 and observations of rare CO isotopomers towardthe rho Ophiuchi molecular cloud

We report the detection of (CO)-C-13-O-17 and present observations of three additional rare CO isotopomers made toward core C of the rho Ophiuchi mole cular cloud. The data encompass single-pointed observations of the J = 1 -- > 0 and J = 2 --> 1 rotational transitions for (CO)-O-18, (CO)-O-17, (CO)-C -13-O-17, and the J = 1 --> 0 transition for (CO)-C-13-O-18. Emission is de tected for all isotopes and transitions observed. For the two O-17-containi ng species, the interstellar spectra display a partially resolved hyperfine spectrum due to the I = 5/2 spin of the O-17 nucleus. The isotope abundanc e ratios derived from these measurements are [C-12]/[C-13] = 65.0 +/- 6.3( stat) +/-9.2(syst) and [O-18]/[O-17] = 4.15 +/- 0.52(stat) +/- 0.59( syst), consistent with recent measurements for nearby molecular clouds. Thus, our measurements support the idea that both ratios are smaller in the local in terstellar medium (ISM) than their terrestrial values of 89 and 5.5.