2001ApJ...562L.185B

We report the detection of ¹³C¹⁷O and present observations of three additional rare CO isotopomers made toward core C of the ρ Ophiuchi molecular cloud. The data encompass single-pointed observations of the J=1⟶0 and J=2⟶1 rotational transitions for C¹⁸O, C¹⁷O, ¹³C¹⁷O, and the J=1⟶0 transition for ¹³C¹⁸O. Emission is detected for all isotopes and transitions observed. For the two ¹⁷O-containing species, the interstellar spectra display a partially resolved hyperfine spectrum due to the I=5/2 spin of the ¹⁷O nucleus. The isotope abundance ratios derived from these measurements are [¹²C]/[¹³C]=65.0±6.3(stat)±9.2(syst) and [¹⁸O]/[¹⁷O]=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 interstellar medium (ISM) than their terrestrial values of 89 and 5.5.