HERSCHEL MEASUREMENTS OF MOLECULAR OXYGEN IN ORION
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
- Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden)
- Centro de Astrobiologia, CSIC-INTA, 28850 Madrid (Spain)
- SETI Institute, Mountain View, CA 94043 (United States)
- Department of Physics and Astronomy, San Jose State University, San Jose, CA 95192 (United States)
- California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 66, Cambridge, MA 02138 (United States)
- Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
- LERMA and UMR8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris (France)
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
- Institute of Astronomy, ETH Zurich, Zurich (Switzerland)
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
- School of Physics and Astronomy, University of Leeds, Leeds (United Kingdom)
- Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France)
- LRA/LERMA, CNRS, UMR8112, Observatoire de Paris and Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris Cedex 05 (France)
We report observations of three rotational transitions of molecular oxygen (O{sub 2}) in emission from the H{sub 2} Peak 1 position of vibrationally excited molecular hydrogen in Orion. We observed the 487 GHz, 774 GHz, and 1121 GHz lines using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory, having velocities of 11 km s{sup -1} to 12 km s{sup -1} and widths of 3 km s{sup -1}. The beam-averaged column density is N(O{sub 2}) = 6.5 x 10{sup 16} cm{sup -2}, and assuming that the source has an equal beam-filling factor for all transitions (beam widths 44, 28, and 19''), the relative line intensities imply a kinetic temperature between 65 K and 120 K. The fractional abundance of O{sub 2} relative to H{sub 2} is (0.3-7.3) x 10{sup -6}. The unusual velocity suggests an association with a {approx}5'' diameter source, denoted Peak A, the Western Clump, or MF4. The mass of this source is {approx}10 M{sub sun} and the dust temperature is {>=}150 K. Our preferred explanation of the enhanced O{sub 2} abundance is that dust grains in this region are sufficiently warm (T {>=} 100 K) to desorb water ice and thus keep a significant fraction of elemental oxygen in the gas phase, with a significant fraction as O{sub 2}. For this small source, the line ratios require a temperature {>=}180 K. The inferred O{sub 2} column density {approx_equal}5 x 10{sup 18} cm{sup -2} can be produced in Peak A, having N(H{sub 2}) {approx_equal} 4 x 10{sup 24} cm{sup -2}. An alternative mechanism is a low-velocity (10-15 km s{sup -1}) C-shock, which can produce N(O{sub 2}) up to 10{sup 17} cm{sup -2}.
- OSTI ID:
- 21579939
- Journal Information:
- Astrophysical Journal, Vol. 737, Issue 2; Other Information: DOI: 10.1088/0004-637X/737/2/96; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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