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Astron. Astrophys. 335, 266-276 (1998)


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Methanol in protostellar outflows

Single-dish and interferometric maps of NGC 1333/IRAS 2

R. Bachiller 1, C. Codella 1, F. Colomer 1, S. Liechti 1 and C.M. Walmsley 2

1 Observatorio Astronómico Nacional (IGN), Apartado 1143, E-28800 Alcalá de Henares (Madrid), Spain
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy

Received 18 December 1997 / Accepted 16 March 1998

Abstract

We report high-resolution mapping observations of the [FORMULA] - [FORMULA], [FORMULA] - [FORMULA], and [FORMULA] - [FORMULA] thermal lines of CH3 OH toward the young bipolar outflow driven by the Class 0 object NGC 1333/IRAS 2. Only weak emission has been detected towards the position of the central object, while strong methanol lines have been observed towards the endpoints of the outflow lobes, where the CH3 OH abundance is enhanced by a factor [FORMULA] 300. The methanol emission is confined in two jets, with a collimation factor of about 20: redshifted emission comes from the south-east lobe, while blueshifted lines are detected towards the north-west. Statistical equilibrium calculations have been used to fit the relative intensities of the observed transitions. These lead us to the conclusion that the ambient gas surrounding the protostar has a density similar to that of the high velocity gas in the shocked regions ([FORMULA] 106 cm-3).

Interferometric maps with a resolution of [FORMULA] show that the blueshifted lobe consists of several "bullets" indicating that episodic mass loss has occurred. The age estimate is [FORMULA] 2-5 103 yr. The high-velocity redshifted emission comes from a structure which becomes "V-like" at velocities close to that of the ambient gas. These results fit nicely with recent magnetohydrodynamical models where a working surface with a cone-like shape creates elongated naked jets containing bullets in their interior.

Key words: stars: formation – ISM: jets and outflows – ISM: individual objects: NGC 1333/IRAS 2 – ISM: molecules – ISM: abundances – radio lines: ISM

Send offprint requests to: R. Bachiller

© European Southern Observatory (ESO) 1998

Online publication: June 12, 1998

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