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Class II CH3OH masers are used as a convenient tracer of disc-like structuresin high-mass star formation. However, more than half of them show a complexdistribution in Very Long Baseline Interferometry (VLBI) maps. The origin ofsuch a complex distribution is still unknown. We conducted VLBI monitoringobservations to unveil the origin of a complex class II CH3OH maser in thehigh-mass star-forming region G59.783+0.065. We observed the CH3OH maser at 6.7GHz and the H2O maser at 22 GHz to probe detailed circumstellar kinematics andstructures by the Japanese VLBI network and the VLBI Exploration of RadioAstrometry. We found similar bipolar distributions in both masers, specificallytwo clusters located 2000 au apart along the East-West direction. We detected alinear distribution of CH3OH masers in the Western cluster. A position-velocitydiagram shows that the Western CH3OH masers trace a rotating disc-wind orinfalling component inside an edge-on disc-like structure. In contrast to thesimple bipolar expanding motions of the H2O masers, the CH3OH masers exhibitedcomplex motions despite their spatial coincidence. Some of the Eastern CH3OHmasers showed bipolar expansions similar to the H2O masers, while othersdisplayed random or even inward motions. Such complex kinematics and theirclose association with the H2O maser could occur at the boundary betweenoutflow and inflow. We suggest that the complex distribution of class II CH3OHmasers, like G59.783+0.065 arises from several distinct circumstellarstructures that simultaneously achieve maser excitation.

A kinematic study of the disc-outflow system around a high-mass protostar G59.783+0.065 probed by methanol and water masers