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Astron. Astrophys. 362, 1093-1108 (2000)


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VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

I. Observational results: protostellar disks or outflows?

V. Minier, R.S. Booth and J.E. Conway

Onsala Space Observatory, 439 92 Onsala, Sweden

Received 16 May 2000 / Accepted 31 August 2000

Abstract

We present VLBI observations of 6.7 and 12.2 GHz methanol masers in 14 star-forming regions, namely NGC 7538, S 252, W 75N, W 48, G 31.28+0.06, S 231, S 255, S 269, Mon R2, G 9.62+0.20, Cep A, W 51, G 59.78+0.06 and G 29.95-0.02. In 10 of these sources, the methanol masers show elongated morphologies in the VLBI map and exhibit linear velocity gradients. These linear structures have lengths of 50 to 1300 AU. We consider whether these structures are consistent with circumstellar disks. Assuming that we see the whole diameter of a Keplerian disk then we derive sub-solar central masses with the exception of W 48. However, it is possible that we only see masers in a fraction of the disk which lies in front of a young massive star. Assuming that the Keplerian disks have diameters of 1000 AU, then the derived enclosed masses vary from 1 to 75 [FORMULA]. We suggest that other models such as accelerating outflows could explain the linear structures; proper motions are needed in order to discriminate between the possible models.

Key words: masers – techniques: interferometric – stars: circumstellar matter – stars: formation – ISM: H ii regions

Send offprint requests to: V. Minier (vincent@oso.chalmers.se)

© European Southern Observatory (ESO) 2000

Online publication: October 30, 2000

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