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P.F. Goldsmith, D. Li (NAIC, Dept. of Astronomy, Cornell Univ.), G.J. Melnick, E.A. Bergin (Center for Astrophysics), J.E. Howe, R.L. Snell (Dept. of Astronomy, Univ. of Massachusetts, Amherst), D.A. Neufeld (Dept. of Physics, Johns Hopkins Univ.), M. Harwit (Dept. of Astronomy, Cornell Univ.)
Deep integrations using the SWAS satellite of the Rho Oph A cloud have resulted in a detection of an emission feature consistent with the NJ = 33 - 12 transition of O2 at a velocity of 5.9 km/s. The line width and velocity are suggestive of the red-shifted wing emission seen in species which trace the molecular outflows seen in this region. The fractional abundance of O2 relative to H2 in this high velocity gas is approximately 10-5. We also report improved upper limits for O2 in several molecular cloud cores, comparable to the lowest results previously obtained, namely N(O2)/N(H2) ~ a few x 10-7. We feel that the most viable scenario explaining the low O2 abundance in cloud cores, along with the much enhanced abundance in the outflow region, is that oxygen atoms are largely depleted onto dust grains in quiescent molecular clouds, but that the shock associated with the outflow restarts gas-phase chemistry, and that after an elapsed time of a few x 105 y, the O2 abundance has increased to the point that this species is one of the main repositories of oxygen atoms. On a somewhat longer time scale, depletion again dominates, and the gas-phase abundance of O2 drops by several orders of magnitude.