EVN observations of 6.7 GHz methanol masers in clusters of massive young
  stellar objects
  Methanol masers at 6.7 GHz are associated with high-mass star-forming regions
(HMSFRs) and often have mid-infrared (MIR) counterparts characterized by
extended emission at 4.5 $\mu$m, which likely traces outflows from massive
young stellar objects (MYSOs). Our objectives are to determine the
milliarcsecond (mas) morphology of the maser emission and to examine if it
comes from one or several candidate MIR counterparts in the clusters of MYSOs.
The European VLBI Network (EVN) was used to image the 6.7 GHz maser line with
~2.'1 field of view toward 14 maser sites from the Torun catalog.
Quasi-simultaneous observations were carried out with the Torun 32 m telescope.
We obtained maps with mas angular resolution that showed diversity of methanol
emission morphology: a linear distribution (e.g., G37.753-00.189), a ring-like
(G40.425+00.700), and a complex one (e.g., G45.467+00.053). The maser emission
is usually associated with the strongest MIR counterpart in the clusters; no
maser emission was detected from other MIR sources in the fields of view of
2.'1 in diameter. The maser source luminosity seems to correlate with the total
luminosity of the central MYSO. Although the Very Long Baseline Interferometry
(VLBI) technique resolves a significant part of the maser emission, the
morphology is still well determined. This indicates that the majority of maser
components have compact cores.
