Water maser variability in a high-mass YSO outburst

Context. Clarifying the relationship between mass accretion and ejection history is one of key issues in understanding high-mass star formation processes. Aims. We aim to investigate possible burst event mid-June 2015 jet protostar S255 NIRS 3. Methods. The Very Long Baseline Interferometer (VLBI) monitoring observations 22 GHz H 2 O masers were carried out using VLBI Exploration Radio Astrometry (VERA) reveal 3D velocity spatial structure outflow/jet traced by In addition, we conducted follow-up submillimeter continuum 321 with Atacama Large Millimeter/submillimeter Array (ALMA) at Band 7. Results. successfully measured proper motions associated a bipolar outflow. almost same as was observed 2005 2010. expansion blueshifted bow shock be 28 km s −1 , corresponding dynamical timescale 60 yr. direction maser outflow slightly tilted compared radio jet, which could suggest more recent episode during event. total flux density gradually increases from beginning early 2017 becomes constant subsequent single-dish 2018. brightening prominent northeast lobe. For first time, revealed extended emission star-forming region, partly resolved VERA even most (VLA) configurations. find that variation such an component similar unresolved emission. ALMA 7 did not show significant variations previous performed five months before. mapped 3 providing fourth example, for this maser, distribution region. Conclusions. conclude features unlikely originate interface powered outburst surrounding medium. due radiative excitation photons form (declining) infrared (IR) escaping along cavity created newly ejected material. lower ratio GHz/321 luminosity suggests temperature ( >1000 K), higher than other