标题： 围绕大质量原恒星 W75N(B)-VLA1 和 W75N(B)-VLA2 的偏振$H_{2}O$量子放大器辐射的监测 显示英文标题

标题： Monitoring of the polarized $H_{2}O$ maser emission around the massive protostars W75N(B)-VLA1 and W75N(B)-VLA2

摘要： 在HMSFR W75N(B)中已经检测到多个射电源，其中大质量的YSOs VLA1和VLA2特别引人关注。这些被认为是处于不同的演化阶段。特别是，VLA1处于电离辐射的早期阶段，并且驱动着一个热射电喷流，而VLA2则是一个热的、准直的电离风，被尘埃盘或包层包围。在这两个射电源中，过去都检测到了22 GHz的水脉泽。围绕VLA1的水脉泽显示出沿射电喷流持续分布，而围绕VLA2的水脉泽则追踪了在20年期间从非准直到准直的喷流演化过程。通过在6年时间内监测围绕VLA1和VLA2的水脉泽的偏振发射，我们旨在确定脉泽分布是否随时间变化，以及磁场是否相应地变化。EVN被用于全偏振和相位参考模式，以测量脉泽的绝对位置，并确定磁场的方向和强度。我们从2014年至2020年每隔两年观测了四个时期。我们在所有时期都检测到了围绕这两个YSOs的水脉泽的偏振发射。我们发现，围绕VLA1的脉泽正在追踪由热射电喷流膨胀产生的非解离冲击，而围绕VLA2的脉泽则正在追踪气体的不对称膨胀，在东北方向气体可能遇到非常致密的介质而停止。我们还发现，每个时期从水脉泽推断出的磁场可以被视为该位置估算的准静态磁场的一部分，而不是该时间点的磁场。这使我们能够通过将所有时期的矢量整体考虑，研究这两个YSOs周围更大区域的磁场形态。 显示英文摘要

摘要： Several radio sources have been detected in the HMSFR W75N(B), among them the massive YSOs VLA1 and VLA2 are of great interest. These are thought to be in different evolutionary stages. In particular, VLA1 is at the early stage of the photoionization and it is driving a thermal radio jet, while VLA2 is a thermal, collimated ionized wind surrounded by a dusty disk or envelope. In both sources 22 GHz water masers have been detected in the past. Those around VLA1 show a persistent distribution along the radio jet and those around VLA2 have instead traced the evolution from a non-collimated to a collimated outflow over a period of 20 years. By monitoring the polarized emission of the water masers around both VLA1 and VLA2 over a period of 6 years, we aim to determine whether the maser distributions show any variation over time and whether the magnetic field behaves accordingly. The EVN was used in full polarization and phase-reference mode to measure the absolute positions of the masers and to determine both the orientation and the strength of the magnetic field. We observed four epochs separated by two years from 2014 to 2020. We detected polarized emission from the water masers around both the YSOs in all the epochs. We find that the masers around VLA1 are tracing a nondissociative shock originating from the expansion of the thermal radio jet, while the masers around VLA2 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 water 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 locally the morphology of the magnetic field around both YSOs in a larger area by considering the vectors estimated in all the epochs as a whole.