Study unreachable — Imaging the milliarcsecond structures of the methanol masers using the European VLBI Network

Abstract

The maser emission of methanol molecule at 6668.519 MHz (ca. 4.5 cm) is exclusively associated with high-mass star forming regions. It is an excellent tracer of still accreting high-mass protostars and, when observed with high angular resolution using the Very Long Baseline Interferometry (VLBI) technique, provides useful information on the morphology and kinematics of the circumstellar gas. It reaches regions that are not easy for studies at other wavelength ranges and enables to learn about a very early stage of massive star formation. We present a review of main results for a sample of 63 high-mass young stellar objects that were discovered in the Galactic plane survey with the 32 m Torun radio telescope and were followed by interferometric observations using the European VLBI Network. The images of the masing regions are obtained and their morphologies are classified as: simple, arc, ring, pair and complex ones. The milliarcsecond structures are studied in details and characteristics of single maser clouds, as their sizes and velocities, are determined. Our main conclusion is that the methanol masers can originate in the disk and/or in the root of outflows.