HERSCHEL HIFI OBSERVATIONS OF O-2 TOWARD ORION: SPECIAL CONDITIONS FOR SHOCK ENHANCED EMISSION
Journal article, 2014
We report observations of molecular oxygen (O-2) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O-2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km s(-1) with line widths similar to 3 km s(-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-2 emission is similar or equal to 9" (6 x 10(16) cm) in size, and is located close to the H-2 Peak 1 position (where vibrationally excited H-2 emission peaks), and not at Peak A, 23" away. The peak O-2 column density is similar to 1.1 x 10(18) cm(-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-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 x 10(4) cm(-3), if a reasonable flux of UV radiation is present. The postshock O-2 can explain the emission from the source if its line-of-sight dimension is similar or equal to 10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O-2 emission has not been detected in the cores of other massive star-forming molecular clouds.
line survey
wave-astronomy-satellite
interstellar molecular clouds
aperture synthesis
massive stars
cologne database
hot core
star-formation
rho-ophiuchi
temporal evolution
Author
Jo-Hsin Chen
Jet Propulsion Laboratory, California Institute of Technology
Paul F. Goldsmith
Jet Propulsion Laboratory, California Institute of Technology
Serena Viti
University College London (UCL)
Ronald Snell
University of Massachusetts
D. Lis
Pierre and Marie Curie University (UPMC)
California Institute of Technology (Caltech)
A.O. Benz
Swiss Federal Institute of Technology in Zürich (ETH)
E. A. Bergin
University of Michigan
John H Black
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
P. Caselli
Max Planck Society
P. J. Encrenaz
Centre national de la recherche scientifique (CNRS)
E. Falgarone
Centre national de la recherche scientifique (CNRS)
Javier R. Goicoechea
Spanish National Research Council (CSIC)
Åke Hjalmarson
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
David Hollenbach
SETI Institute
Michael J. Kaufman
San Jose State University
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
D. A. Neufeld
Johns Hopkins University
Laurent Pagani
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
F. F. S. van der Tak
Netherlands Institute for Space Research (SRON)
University of Groningen
E. F. van Dishoeck
Leiden University
Max Planck Society
U. A. Yildiz
Jet Propulsion Laboratory, California Institute of Technology
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 793 2 Article nr. 111 - 111Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1088/0004-637X/793/2/111