HERSCHEL HIFI OBSERVATIONS OF O-2 TOWARD ORION: SPECIAL CONDITIONS FOR SHOCK ENHANCED EMISSION
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.

temporal evolution

massive stars

interstellar molecular clouds

line survey

hot core

star-formation

aperture synthesis

cologne database

wave-astronomy-satellite

rho-ophiuchi

Författare

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

Universite Pierre et Marie Curie

CalTech

A.O. Benz

Eidgenössische Technische Hochschule Zürich (ETH)

E. A. Bergin

University Michigan Ann Arbor

John H Black

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

P. Caselli

Max Planck-institutet

P. J. Encrenaz

CNRS Centre National de la Recherche Scientifique

E. Falgarone

CNRS Centre National de la Recherche Scientifique

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

SRON Netherlands Institute for Space Research

University of Groningen, Kapteyn Astronomical Institute

E. F. van Dishoeck

Max Planck-institutet

Leiden University

U. A. Yildiz

Jet Propulsion Laboratory, California Institute of Technology

Astrophysical Journal

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

Vol. 793 Article nr. 111 - 111

Ämneskategorier

Astronomi, astrofysik och kosmologi

DOI

10.1088/0004-637X/793/2/111