Astronomy and Astrophysics, volume 525A, 120-120 (2011/1-1)
VLA observations of water masers towards 6.7GHz methanol maser sources.
BARTKIEWICZ A., SZYMCZAK M., PIHLSTROEM Y.M., VAN LANGEVELDE H.J., BRUNTHALER A. and REID M.J.
Abstract (from CDS):
Both 22GHz water and 6.7GHz methanol masers are usually interpreted as signposts of early stages of high-mass star formation but little is known about their associations and the physical environments in which they occur. We attempt to derive accurate positions and morphologies of the water maser emission and relate them to the methanol maser emission mapped earlier with Very Long Baseline Interferometry. We searched for 22GHz water masers in 31 methanol maser sources was searched for 22GHz water masers using the VLA and observed in the 6.7GHz methanol maser line with the 32m Torun dish simultaneously. Water maser clusters are detected towards 27 sites leading to the identification of 15 new sources. The detection rate of water maser emission associated with methanol sources is as high as 71%. In a large number of objects (18/21), the structure of water maser is well aligned with that of the extended emission at 4.5µm confirming the origin of water emission in outflows. The sources of methanol emission with ring-like morphologies, which likely trace a circumstellar disc/torus, either do not show associated water masers or the distribution of water maser spots is orthogonal to the major axis of the ring. The two maser species are generally powered by the same high-mass young stellar object but probe different parts of its environment. The morphology of water and methanol maser emission in a minority of sources is consistent with a scenario where 6.7GHz methanol masers trace a disc/torus around a protostar while the associated 22GHz water masers arise in outflows. The majority of sources in which methanol maser emission is associated with the water maser appear to trace outflows. The two types of associations may be related to different evolutionary phases.