2014A&A...565L...8S

W75N(B) is a massive star-forming region that contains three radio continuum sources (VLA1, VLA2, and VLA3), which are thought to be three massive young stellar objects at three different evolutionary stages. VLA1 is the most evolved and VLA2 the least evolved source. The 22GHz H₂O masers associated with VLA1 and VLA2 have been mapped at several epochs over eight years. While the H₂O masers in VLA1 show a persistent linear distribution along a radio jet, those in VLA2 are distributed around an expanding shell. Furthermore, H₂O maser polarimetric measurements revealed magnetic fields aligned with the two structures. Using new polarimetric observations of H₂O masers, we aim to confirm the elliptical expansion of the shell-like structure around VLA2 and, at the same time, to determine if the magnetic fields around the two sources have changed. The NRAO Very Long Baseline Array was used to measure the linear polarization and the Zeeman-splitting of the 22GHz H₂O masers towards the massive star-forming region W75N(B). The H₂O maser distribution around VLA1 is unchanged from that previously observed. We made an elliptical fit of the H₂O masers around VLA2. We find that the shell-like structure is still expanding along the direction parallel to the thermal radio jet of VLA1. While the magnetic field around VLA1 has not changed in the past ∼7 years, the magnetic field around VLA2 has changed its orientation according to the new direction of the major-axis of the shell-like structure and it is now aligned with the magnetic field in VLA1.