Context. The 6.7 GHz methanol maser marks an early stage of high-mass star formation, but the origin of this maser is currently a matter of debate. In particular it is unclear whether the maser emission arises in discs, outflows or behind shocks running into rotating molecular clouds. Aims. We investigated which structures the methanol masers trace in the environment of high-mass protostar candidates by observing a homogenous sample of methanol masers selected from Torun surveys. We also probed their origins by looking for associated H II regions and IR emission. Methods. We selected 30 methanol sources with improved position accuracies achieved using MERLIN and another 3 from the literature. We imaged 31 of these using the European VLBI Network's expanded array of telescopes with 5-cm (6-GHz) receivers. We used the VLA to search for 8.4 GHz radio continuum counterparts and inspected Spitzer GLIMPSE data at 3.6-8 μm from the archive. Results. High angular resolution images allowed us to analyze the morphology and kinematics of the methanol masers in great detail and verify their association with radio continuum and mid-infrared emission. A new class of "ring-like" methanol masers in starforming regions appeared to be suprisingly common, 29% of the sample. Conclusions. The new morphology strongly suggests that methanol masers originate in the disc or torus around a proto-or a young massive star. However, the maser kinematics indicate the strong influence of outflow or infall. This suggests that they form at the interface between the disc/torus and a flow. This is also strongly supported by Spitzer results because the majority of the masers coincide with 4.5 μm emission to within less than 1 . Only four masers are associated with the central parts of UC H II regions. This implies that 6.7 GHz methanol maser emission occurs before H II region observable at cm wavelengths is formed.

We report the first results of a search for 6.7 GHz methanol masers in the direction of 1399 IRAS objects north of declination −20 • with the flux densities greater than 100 Jy at 60 µm and the flux density ratio F 60 /F 25 > 1. Observations were made with the sensitivity of 1.7 Jy and the velocity resolution of 0.04 km s −1 using the 32-m Toruń radio telescope. Maser emission was found in 182 sources, including 70 new detections. 32 new sources were identified with objects of radio emission associated with star-forming regions. Comparison of the present data set with other observations suggests that about 65% of methanol masers exhibit moderate or strong variations on timescales of about 4 and 8 years.

Abstract. We report the results of an unbiased survey for 6.7 GHz methanol maser emission of a ∼21 deg 2 strip of the Galactic plane carried out with the 32 m Toruń radio telescope. An area at 20• ≤ l ≤ 40• , |b| ≤ 0.• 52 was surveyed in an equilateral triangular grid with a sensitivity limit of about 1.6 Jy. We detected a total of 100 sources, 26 of which are new detections. All the new sources are of moderate intensity and their peak flux densities have median value of 6.5 Jy, i.e. about half that of previously known sources in the sample. About 80% of maser sources have IR counterpart candidates within a 1 radius but not all the IRAS counterparts of methanol masers have colours typical of ultracompact HII regions. An excess of masers unassociated with IR sources occurs at 30• because of incompleteness of IR catalogues due to strong confusion near the tangential region of the spiral arm. Our unbiased survey doubled the number of detections as compared to IRAS-based observations. Within the positional uncertainty of 1 about one third of the methanol sources have radio continuum counterparts at 5 GHz of a flux density greater than 2.5-10 mJy. The distribution of methanol sources appears to be consistent with a clustered mode of formation of massive stars.

Abstract.The 22 GHz H 2 O maser line was observed towards 79 candidate high-mass protostellar objects from a flux-limited sample of 6.7 GHz methanol sources. The emission was detected in 41 sources, towards 28 of these for the first time. The detection rate of 52% was similar to rates reported for other samples of high-mass protostars selected mainly with far-infrared (FIR) colour criteria. The median value of H 2 O maser luminosity of 10 −5.5 L is equal to that of the CH 3 OH maser luminosity, whereas the median OH maser luminosity was found to be ∼1.5 orders of magnitude lower. Comparison of the velocity ranges showing maser emission implies that for the majority of sources the H 2 O and CH 3 OH maser lines originate from different regions. The percentage of sources with emission in two or three of the maser species, their association with radio continuum and IR emission and the maser and IR luminosities are consistent with the view that evolutionary phases with H 2 O and CH 3 OH masers largely overlap and precede the OH maser phase, while at a later stage OH and CH 3 OH masers may coexist. Strong correlations of OH and CH 3 OH maser luminosities with IR luminosity and only a marginal correlation of H 2 O and IR luminosity confirm current pumping schemes of all three maser lines.