First Tentative Detection of the Molecular Oxygen Isotopomer 16/O/18/O in Interstellar Clouds

Details First Tentative Detection of the Molecular Oxygen Isotopomer 16/O/18/O in Interstellar Clouds First Tentative Detection of the Molecular Oxygen Isotopomer 16/O/18/O in Interstellar Clouds

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...274l..13p&link_type=abstract

Astronomy and Astrophysics, Vol. 274, NO. 1/JUL(I), P. L13, 1993

Astronomy and Astrophysics

Astrophysics

17

Line: Identification, Ism: Abundances, Ism Individual Objects: L134N, Ngc 7538, Ism: Molecules, Radio Lines: Interstellar

Scientific paper

We report the first tentative detection of molecular oxygen in interstellar clouds by observation of the 234 GHz (N,J) = (2,1) - (0,1) line of the isotopomer 16O18O towards L134N. The line has a peak intensity of 18±6 mK and an integrated intensity of 5.3±1.8 mK km s-1. Two other lines are present within the 12CO linewidth which are probably unidentified lines, but could arise from other weaker clumps. We also detected a feature in NGC 7538 in our first observing run with a peak intensity of 10.0±2.2 mK and an integrated intensity of 13±2 mK km s-1. However, we could not confirm this detection during our last observing session and, although we checked that this is not a telluric line, we believe that this line is suspicious. The ratio of 16O18O/C18O in L134N is 0.8 if we restrict the C18O column density to the 16O18O linewidth and 0.4 using the entire C18O line. The corresponding O2/CO ratio (0.2 to 0.4) implies that the fractional abundance of gaseous oxygen is about (4-8) × 10-5, in agreement with gas phase chemical models. We also observed two other cold dark clouds (B5 and TMC 2) but without success; our upper limits for these sources are significantly below those reported previously but above our tentative detection in L134N.

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