We have used the Australia Telescope Compact Array (ATCA) to make high-resolution images of the 6.7-GHz 51 → 60A+ maser transition of methanol towards 33 sources in the Galactic plane. Including the results from 12 methanol sources in the literature, we find that 17 out of 45 sources have curved or linear morphology. Most of the 17 have a velocity gradient along the line, which is consistent with masers lying in an edge-on circumstellar disc surrounding a massive star. We also made simultaneous continuum observations of the sources at 8.6 GHz, in order to image any associated H II region. 25 of the sources are associated with an ultracompact H II region, with a detection limit of ∼0.5 mJy beam-1. We argue that the methanol sources without an associated H II region represent less massive embedded stars, not an earlier stage in the lifetime of the star, as previously suggested.

Item Type:	Refereed Article
Research Division:	Physical Sciences
Research Group:	Astronomical and Space Sciences
Research Field:	Galactic Astronomy
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in the Physical Sciences
UTAS Author:	Phillips, CJ (Dr Christopher Phillips)
UTAS Author:	Ellingsen, SP (Professor Simon Ellingsen)
UTAS Author:	McCulloch, PM (Professor Peter McCulloch)
ID Code:	13571
Year Published:	1998
Web of Science® Times Cited:	121
Deposited By:	Physics
Deposited On:	1998-08-01
Last Modified:	2011-08-08
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