Artikel i vetenskaplig tidskrift, 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.

hot core



cologne database

interstellar molecular clouds

aperture synthesis

line survey

massive stars


temporal evolution


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

Université Pierre et Marie Curie (UPMC)

California Institute of Technology (Caltech)

A.O. Benz

Eidgenössische Technische Hochschule Zürich (ETH)

E. A. Bergin

University of Michigan

John H Black

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

P. Caselli


P. J. Encrenaz

Centre national de la recherche scientifique (CNRS)

E. Falgarone

Centre national de la recherche scientifique (CNRS)

Javier R. Goicoechea

CSIC - Instituto de Ciencia de Materiales de Madrid (ICMM)

Åke Hjalmarson

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

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

Rijksuniversiteit Groningen

Netherlands Institute for Space Research (SRON)

E. F. van Dishoeck


Universiteit Leiden

U. A. Yildiz

Jet Propulsion Laboratory, California Institute of Technology

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 793 2 Article nr. 111 - 111


Astronomi, astrofysik och kosmologi



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