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Título: | Monitoring of the polarized H2O maser emission around the massive protostars W75N(B)-VLA 1 and W75N(B)-VLA 2 |
Autor: | Surcis, G.; Vlemmings, W. H. T.; Goddi, C.; Torrelles, José M. CSIC ORCID; Gómez, José L. CSIC ORCID ; Rodríguez-Kamenetzky, Adriana; Carrasco-González, C.; Curiel, Salvador; Kim, S. W.; Kim, J. S.; Langevelde, H. J. van | Palabras clave: | Stars: formation Masers Polarization Magnetic fields |
Fecha de publicación: | 24-abr-2023 | Editor: | EDP Sciences | Citación: | Astronomy and Astrophysics 673: A10 (2023) | Resumen: | [Context] Several radio sources have been detected in the high-mass star-forming region W75N(B), with the massive young stellar objects VLA 1 and VLA 2 shown to be of particular interest among them. These objects are thought to be at different evolutionary stages: VLA 1 is in the early stage of photoionization and driving a thermal radio jet, while VLA 2 is a thermal, collimated ionized wind surrounded by a dusty disk or envelope. In both sources, 22 GHz H2O masers have been detected in the past. Those around VLA 1 show a persistent linear distribution along the thermal radio jet, while those around VLA 2 have traced the evolution from a non-collimated to a collimated outflow over a period of ∼20 yr. The magnetic field inferred from the H2O masers has shown an orientation rotation following the direction of the major-axis of the shell around VLA 2, whereas it is immutable around VLA 1. [Aims] By monitoring the polarized emission of the 22 GHz H2O masers around both VLA 1 and VLA 2 over a period of six years, we aim to determine whether the H2O maser distributions show any variation over time and whether the magnetic field behaves accordingly. [Methods] The European VLBI Network was used in full polarization and phase-reference mode in order to determine the absolute positions of the 22 GHz H2O masers with a beam size of ∼1 mas and to determine the orientation and the strength of the magnetic field. We observed four epochs separated by two years from 2014 to 2020. [Results] We detected polarized emission from the H2O masers around both VLA 1 and VLA 2 in all the epochs. By comparing the H2O masers detected in the four epochs, we find that the masers around VLA 1 are tracing a nondissociative shock originating from the expansion of the thermal radio jet, while the masers around VLA 2 are tracing an asymmetric expansion of the gas that is halted in the northeast where the gas likely encounters a very dense medium. We also found that the magnetic field inferred from the H2O masers in each epoch can be considered as a portion of a quasi-static magnetic field estimated in that location rather than in that time. This allowed us to study the morphology of the magnetic field around both VLA 1 and VLA 2 locally across a larger area by considering the vectors estimated in all the epochs as a whole. We find that the magnetic field in VLA 1 is located along the jet axis, bending toward the north and south at the northeasterly and southwesterly ends of the jet, respectively, reconnecting with the large-scale magnetic field. The magnetic field in VLA 2 is perpendicular to the expansion directions until it encounters the denser matter in the northeast, where the magnetic field is parallel to the expansion direction and agrees with the large-scale magnetic field. We also measured the magnetic field strength along the line of sight in three of the four epochs, with resulting values of −764 mG < B||VLA 1 < − 676 mG and −355 mG < B||VLA 2 < −2426 mG. |
Versión del editor: | http://dx.doi.org/10.1051/0004-6361/202245734 | URI: | http://hdl.handle.net/10261/331442 | DOI: | 10.1051/0004-6361/202245734 | ISSN: | 0004-6361 | E-ISSN: | 1432-0746 |
Aparece en las colecciones: | (IAA) Artículos (ICE) Artículos |
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2023A&A...674A..62R.pdf | 1,09 MB | Adobe PDF | Visualizar/Abrir |
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