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

Jo-Hsin Chen ; Paul F. Goldsmith ; Serena Viti ; Ronald Snell ; Dariusz C. Lis ; Arnold Benz ; Edwin Bergin ; John H. Black (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; Paola Caselli ; Pierre Encrenaz ; Edith Falgarone ; Javier R. Goicoechea ; Åke Hjalmarson (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; David Hollenbach ; Michael Kaufman ; Gary Melnick ; David Neufeld ; Laurent Pagani ; Floris van der Tak ; Ewine van Dishoeck ; Umut A. Yildiz
Astrophysical Journal (0004-637X). Vol. 793 (2014), 2, p. Article nr. 111 .
[Artikel, refereegranskad vetenskaplig]

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.

Nyckelord: interstellar molecular clouds, wave-astronomy-satellite, temporal evolution, hot core, aperture synthesis, cologne database, star-formation, massive stars, rho-ophiuchi, line survey



Denna post skapades 2014-11-13. Senast ändrad 2015-07-10.
CPL Pubid: 205754

 

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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik (2010-2017)

Ämnesområden

Astronomi, astrofysik och kosmologi

Chalmers infrastruktur