Herschel Measurements of Molecular Oxygen in Orion
Journal article, 2011
We report observations of three rotational transitions of molecular oxygen (O2) in emission from the H2 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–1 to 12 km s–1 and widths of 3 km s–1. The beam-averaged column density is N(O2) = 6.5 × 1016 cm–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 O2 relative to H2 is (0.3-7.3) × 10–6. The unusual velocity suggests an association with a ~5'' diameter source, denoted Peak A, the Western Clump, or MF4. The mass of this source is ~10 Msun and the dust temperature is ≥150 K. Our preferred explanation of the enhanced O2 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 O2. For this small source, the line ratios require a temperature ≥180 K. The inferred O2 column density sime5 × 1018 cm–2 can be produced in Peak A, having N(H2) sime 4 × 1024 cm–2. An alternative mechanism is a low-velocity (10-15 km s–1) C-shock, which can produce N(O2) up to 1017 cm–2.
astrochemistry
interstellar molecules
submillimeter
interstellar medium
Author
Paul F. Goldsmith
Jet Propulsion Laboratory, California Institute of Technology
René Liseau
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
Tom A. Bell
Centro de Astrobiologia (CAB)
John H Black
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
Jo-Hsin Chen
Jet Propulsion Laboratory, California Institute of Technology
David Hollenbach
SETI Institute
Michael J. Kaufman
San Jose State University
Di Li
Jet Propulsion Laboratory, California Institute of Technology
D. Lis
California Institute of Technology (Caltech)
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
Ronald Snell
University of Massachusetts
A. O. Benz
Swiss Federal Institute of Technology in Zürich (ETH)
E. A. Bergin
University of Michigan
S. Bruderer
Swiss Federal Institute of Technology in Zürich (ETH)
P. Caselli
University of Leeds
E. Caux
Centre national de la recherche scientifique (CNRS)
University of Toulouse
P. J. Encrenaz
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
E. Falgarone
Centre national de la recherche scientifique (CNRS)
M. Gerin
Centre national de la recherche scientifique (CNRS)
Javier R. Goicoechea
Centro de Astrobiologia (CAB)
Åke Hjalmarson
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
Bengt Larsson
Stockholm Observatory
Jacques Le Bourlot
LUTH - Laboratoire de l'Univers et de ses Theories
Franck Le Petit
LUTH - Laboratoire de l'Univers et de ses Theories
Massimo De Luca
LUTH - Laboratoire de l'Univers et de ses Theories
Zsofia Nagy
University of Groningen
Evelyne Roueff
LUTH - Laboratoire de l'Univers et de ses Theories
A. Sandqvist
Stockholm Observatory
F. F. S. van der Tak
University of Groningen
E. F. van Dishoeck
Max Planck Society
Leiden University
Charlotte Vastel
Centre national de la recherche scientifique (CNRS)
University of Toulouse
Serena Viti
University College London (UCL)
U. A. Yildiz
Leiden University
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 737 2 96 (1-17) 96Subject Categories
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.1088/0004-637X/737/2/96