2021PASJ...73.1669T

We observed H₂O (6₁₆-5₂₃) maser emission associated with the high-mass star-forming region IRAS 23139+5959 using the KaVA, a combination of very long baseline interferometry (VLBI) arrays between the Korean VLBI Network and the VLBI Exploration of Radio Astrometry (Japan). Through multi-epoch KaVA observations, we detected three groups of maser features, two of which coincide with those previously detected by the Karl G. Jansky Very Large Array. By determining the maser proper motions, we found that the first of maser groups exhibits an expanding motion that traces a wide-angle outflow almost along the line of sight, while the second one seems to be associated with the envelope of an H II region. We discuss the star formation activity in IRAS 23139+5939, which may be reflected in the high variability of H₂O masers associated with an outflow seen from the front.