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Title: Herschel HIFI observations of O{sub 2} toward Orion: special conditions for shock enhanced emission

We report observations of molecular oxygen (O{sub 2}) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O{sub 2} lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km s{sup –1} with line widths ∼3 km s{sup –1}; however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O{sub 2} emission is ≅9'' (6 × 10{sup 16} cm) in size, and is located close to the H {sub 2} Peak 1 position (where vibrationally excited H{sub 2} emission peaks), and not at Peak A, 23'' away. The peak O{sub 2} column density is ≅1.1 × 10{sup 18} cm{sup –2}. The line velocity is close to that of the 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line of sight. The enhanced O{sub 2} abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velocity C shockmore » through a clump with preshock density 2 × 10{sup 4} cm{sup –3}, if a reasonable flux of UV radiation is present. The postshock O{sub 2} can explain the emission from the source if its line-of-sight dimension is ≅10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O{sub 2} emission has not been detected in the cores of other massive star-forming molecular clouds.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ; ;  [7] ;  [8] ; ;  [9] ;  [10] ;  [11] ;  [12] ;  [13] ;  [14] ;  [15] ;
  1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
  2. Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)
  3. Department of Astronomy, University of Massachusetts, LGRT-B 619E, 710 North Pleasant Street, Amherst, MA 01003 (United States)
  4. California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125 (United States)
  5. Institute of Astronomy, ETH Zurich, Zurich (Switzerland)
  6. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
  7. Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden)
  8. Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching (Germany)
  9. LRA/LERMA, CNRS, UMR8112, Observatoire de Paris and École Normale Supérieure, 24 rue Lhomond, F-75231 Paris Cedex 05 (France)
  10. Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), E-28049, Cantoblanco, Madrid (Spain)
  11. SETI Institute, Mountain View, CA 94043 (United States)
  12. Department of Physics and Astronomy, San José State University, San Jose, CA 95192 (United States)
  13. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 66, Cambridge, MA 02138 (United States)
  14. Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
  15. LERMA and UMR8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, F-75014, Paris (France)
Publication Date:
OSTI Identifier:
22370565
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 793; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; COSMIC GASES; DENSITY; ELEMENT ABUNDANCE; EMISSION; GAIN; GHZ RANGE; HYDROGEN; INTERSTELLAR SPACE; LINE WIDTHS; MASERS; MOLECULES; OXYGEN; SHOCK WAVES; STARS; ULTRAVIOLET RADIATION; VELOCITY