HAL : hal-00627666, version 1

arXiv : 1108.0441

Code Bibliographique ADS : 2011ApJ...737...96G

DOI : 10.1088/0004-637X/737/2/96

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The Astrophysical Journal 737 (2011) 96

Herschel Measurements of Molecular Oxygen in Orion

Paul F. Goldsmith, René Liseau 1, Tom A. Bell, John H. Black, Jo-Hsin Chen, David Hollenbach, Michael J. Kaufman, Di Li, Dariusz C. Lis, Gary Melnick, David Neufeld, Laurent Pagani 2, Ronald Snell, Arnold O. Benz, Edwin Bergin 3, Simon Bruderer, Paola Caselli 4, Emmanuel Caux 5, Pierre Encrenaz 2, Edith Falgarone 2, Maryvonne Gerin 2, Javier R. Goicoechea 2, Åke Hjalmarson, Bengt Larsson, Jacques Le Bourlot 6, Franck Le Petit 6, 7, Massimo De Luca 2, Zsofia Nagy, Evelyne Roueff 6, Aage Sandqvist, Floris van der Tak 8, 9, Ewine F. Van Dishoeck, Charlotte Vastel 5, Serena Viti, Umut Yıldız

(08/2011)

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 M sun 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) ~= 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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

1 :	Chalmers University of Technology, Department Radio and Space Science
	Chalmers University of Technology
2 :	Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA)
	CNRS : UMR8112 – INSU – Observatoire de Paris – Université Pierre et Marie Curie [UPMC] - Paris VI – Université de Cergy Pontoise – Ecole normale supérieure de Paris - ENS Paris
3 :	Harvard-Smithsonian Center for Astrophysics
	Harvard-Smithsonian Center for Astrophysics
4 :	Osservatorio Astrofisico di Arcetri (INAF)
	INFN
5 :	Centre d'étude spatiale des rayonnements (CESR)
	CNRS : UMR5187 – Observatoire Midi-Pyrénées – INSU – Université Paul Sabatier [UPS] - Toulouse III
6 :	Laboratoire Univers et Théories (LUTH)
	CNRS : UMR8102 – INSU – Observatoire de Paris – Université Paris VII - Paris Diderot
7 :	Onsala Space Observatory (OSO)
	Chalmers University - Göteborg
8 :	Institute for Space Research Netherlands (SRON)
	SRON Netherlands Institute for Space Research
9 :	Max-Planck-Institut für Radioastronomie (MPIFR)
	Max-Planck-Institut

Domaine

:

Planète et Univers/Astrophysique/Astrophysique galactique Physique/Astrophysique/Astrophysique galactique

Mots Clés : astrochemistry – ISM: abundances – ISM: individual objects: Orion – ISM: molecules – submillimeter: ISM

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Contributeur : Laurent Pagani <>

Soumis le : Jeudi 29 Septembre 2011, 12:01:48

Dernière modification le : Jeudi 29 Septembre 2011, 12:01:48