Herschel HIFI observations of O{sub 2} toward Orion: special conditions for shock enhanced emission
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
- Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)
- Department of Astronomy, University of Massachusetts, LGRT-B 619E, 710 North Pleasant Street, Amherst, MA 01003 (United States)
- California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125 (United States)
- Institute of Astronomy, ETH Zurich, Zurich (Switzerland)
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden)
- Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching (Germany)
- LRA/LERMA, CNRS, UMR8112, Observatoire de Paris and École Normale Supérieure, 24 rue Lhomond, F-75231 Paris Cedex 05 (France)
- Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), E-28049, Cantoblanco, Madrid (Spain)
- SETI Institute, Mountain View, CA 94043 (United States)
- Department of Physics and Astronomy, San José State University, San Jose, CA 95192 (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, F-75014, Paris (France)
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 shock 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.
- OSTI ID:
- 22370565
- Journal Information:
- Astrophysical Journal, Vol. 793, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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