Physics
Scientific paper
Oct 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt........15h&link_type=abstract
Ph.D. Thesis, University of Manchester
Physics
Masers, Methanol-Stars, Formation: Ism, Molecules, Radio Lines:Ism
Scientific paper
Phase-referenced observa tions of OH 4.7-GHz masers in 13 regions of massive star-formation were carried out using MERLIN. Masers were detected in 10 of the regions and the flux-weighted mean positions and velocities of masers were determined. These were compared with published positions and velocities of 1.7-GHz OH masers. Where two lines coincide to 30 AU and 1 km s-1, it is suggested that the masers are propagating through the same column of gas. Incidents of co-propagation can help to constrain models of maser pumping and hence determine the physical conditions within the region. There were 5 OH 4765-MHz masers thought to be co-propagating with OH 1665 or 1720-MHz masers. In one region, W3(OH), MERLIN detected a vast low-brightness OH maser filament that stretches 2200~AU across the face of the HII region and has a systematic velocity gradient. Phase-referenced observations were carried out in W3(OH) using the new MERLIN 6-GHz receivers. 40 methanol 6668-MHz masers were found and several co-propagating maser regions were identified. The methanol masers formed extended arcs and a large-scale analogue to the OH filament. The extended OH and methanol anti-correlate in position, suggesting a change in conditions along the filament. It is likely that the maser arcs and filaments delineate shocks. The velocities of methanol masers in W3(OH) suggest a large-scale rotating disk and groups of masers to the North of the region and the OH filament appear to suggest the region may also be expanding.
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