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Astron. Astrophys. 344, L57-L61 (1999)

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Letter to the Editor

Jets and high-velocity bullets in the Orion A outflows. Is the IRc2 outflow powered by a variable jet?

A. Rodríguez-Franco 1,2, J. Martín-Pintado 2 and T.L. Wilson 3,4

1 Departamento de Matemática Aplicada II, Sección departamental de Optica, Escuela Universitaria de Optica, Universidad Complutense de Madrid. Av. Arcos de Jalón s/n. E-28037 Madrid, Spain
2 Observatorio Astronómico Nacional (IGN), Campus Universitario, Apdo. 1143, E-28800, Alcalá de Henares, Spain
3 Max-Planck-Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany
4 Sub-mm Telescope Observatory, Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA

Received 8 December 1998 / Accepted 5 March 1999


We present high sensitivity maps of the High Velocity (HV) CO emission toward the molecular outflows around IRc2 and Orion-S in the Orion A molecular cloud. The maps reveal the presence of HV bullets in both outflows with velocities between 40-80 km s-1 from the ambient gas velocity. The blue and redshifted CO HV bullets associated with the IRc2 outflow are distributed in thin ([FORMULA], [FORMULA]pc) elliptical ring-like structures with a size of [FORMULA] ([FORMULA]pc). The CO emission at the most extreme blue and redshifted velocities (EHV) peaks [FORMULA] north of source I, just inside the rings of the HV bullets.

The low velocity H2O masers and the [FORMULA] bullets around IRc2 are located at the inner edges of the ring of CO HV bullets and surrounding the EHV CO emission. Furthermore, the high velocity H2O masers are very well correlated with the EHV CO emission. This morphology is consistent with a model of a jet driven molecular outflow oriented close to the line of sight.

In the Orion-S outflow, the morphology of the CO HV bullets shows a bipolar structure in the southeast[FORMULA]northwest direction, and the H2O masers are found only at low velocities in the region between the exciting source and the CO HV bullets.

The morphology of the CO HV bullets, the radial velocities and the spatial distribution of the H2O masers in both outflows, as well as the [FORMULA] features around IRc2, are consistent with a model in which these outflows are driven by a jet variable in direction. In this scenario, the large traverse velocity measured for the H2O masers in the IRc2 outflow, [FORMULA]km s-1, supports the evolutionary connection between the jet and the shell-like outflows.

Key words: ISM: clouds – ISM: individual objects: Orion A – ISM: jets and outflows – stars: formation – stars: mass-loss

Send offprint requests to: A. Rodríguez-Franco to the IGN address

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© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999