Rapidly increasing collimation and magnetic field changes of a H2O maser outflow

Abstract

W75N(B) is a massive star-forming region that contains three radio continuum sources (VLA 1, VLA 2, and VLA 3), which are thought to be three massive young stellar objects at three different evolutionary stages. VLA 1 is the most evolved and VLA 2 the least evolved source. The 22 GHz H2O masers associated with VLA 1 and VLA 2 have been mapped at several epochs over eight years. While the H2O masers in VLA 1 show a persistent linear distribution along a radio jet, those in VLA 2 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 VLA 2 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 22 GHz H2O masers towards the massive star-forming region W75N(B). The H2O maser distribution around VLA 1 is unchanged from that previously observed. We made an elliptical fit of the H2O masers around VLA 2. We find that the shell-like structure is still expanding along the direction parallel to the thermal radio jet of VLA 1. While the magnetic field around VLA 1 has not changed in the past 7 years, the magnetic field around VLA 2 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 VLA 1.

arXiv comment10 pages (5 + online material), 3 figures, 4 tables, accepted by Astronomy & Astrophysics Letter

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Cited by in corpus (13)

• Radio Jets from Young Stellar Objects
• Observing the onset of outflow collimation in a massive protostar
• A Catalog of Methanol Masers in Massive Star-forming Regions. III. The Molecular Outflow Sample
• Zooming into the Collimation Zone in a Massive Protostellar Jet
• Measuring Magnetic Fields from Water Masers in the Synchrotron Protostellar Jet in W3(H${}_2$O)
• EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions IV. Magnetic field strength limits and structure for 7 additional sources
• Methanol masers reveal the magnetic field of the high-mass protostar IRAS 18089-1732
• Characterizing the radio continuum nature of sources in the massive star-forming region W75N (B)
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• EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions. V. Completion of the flux-limited sample
• Resolving the collimation zone of an intermediate-mass protostar
• Polarized Maser Emission with In-Source Faraday Rotation
• The magnetic field of a magnetohydrodynamic disk wind: Water maser observations and simulations