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arXiv 1107.5313astro-ph.SR
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NGC7538-IRS1的H2O和CH3OH脉泽环境的性质和偏振

The properties and polarization of the H2O and CH3OH maser environment of NGC7538-IRS1

G. Surcis, W. H. T. Vlemmings, R. M. Torres, H. J. van Langevelde, B. Hutawarakorn Kramer

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13 pages, 9 figures, 4 Tables, accepted by Astronomy & Astrophysics
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摘要：

NGC 7538是一个复杂的大质量恒星形成区。该地区是由几个无线电连续源，其中之一是IRS 1，一个高质量的原恒星，从0.3 pc的分子双极流出检测。在IRS 1周围发现了几种脉泽。CH_3OH脉泽被认为是追踪开普勒盘，而H_2 O脉泽几乎与外流成一直线。最近的结果表明，该区域拥有一个环面和潜在的磁盘，但与开普勒磁盘不同的倾斜度，应该是由CH 3OH脉泽跟踪。追踪原恒星附近的磁场是确定盘/环取向的基础。最近的研究表明，在大质量恒星形成的原恒星阶段，磁场的方向沿着外流方向，围绕着盘/环的表面或在其表面上。在毫角秒分辨率下对偏振脉泽辐射的观测可以为理解磁场的方向以及NGC 7538-IRS 1中圆盘/环面的方向做出至关重要的贡献。利用NRAO甚长基线阵测量了22 GHz水脉泽对NGC 7538-IRS 1的线偏振和塞曼分裂。利用欧洲VLBI网和MERLIN望远镜对6.7GHz CH_3OH脉泽的线偏振和塞曼分裂进行了测量。我们在高角分辨率下探测到17个H_2O脉泽和49个CH_3OH脉泽。我们探测到了两个水脉泽和二十个甲醇脉泽的线性偏振辐射。CH 3OH脉泽，其中大部分只显示了核心结构，似乎跟踪旋转和潜在的落入气体的内部部分的环面。在三个甲醇脉泽中测量到了显著的塞曼分裂。[...]我们还对NGC 7538-IRS 1脉泽区的结构提出了新的描述。

英文摘要：

NGC7538 is a complex massive star-forming region. The region is composed of several radio continuum sources, one of which is IRS1, a high-mass protostar, from which a 0.3 pc molecular bipolar outflow was detected. Several maser species have been detected around IRS1. The CH3OH masers have been suggested to trace a Keplerian-disk, while the H2O masers are almost aligned to the outflow. More recent results suggested that the region hosts a torus and potentially a disk, but with a different inclination than the Keplerian-disk that is supposed to be traced by the CH3OH masers. Tracing the magnetic field close to protostars is fundamental for determining the orientation of the disk/torus. Recent studies showed that during the protostellar phase of high-mass star formation the magnetic field is oriented along the outflows and around or on the surfaces of the disk/torus. The observations of polarized maser emissions at milliarcsecond resolution can make a crucial contribution to understanding the orientation of the magnetic field and, consequently, the orientation of the disk/torus in NGC7538-IRS1. The NRAO Very Long Baseline Array was used to measure the linear polarization and the Zeeman-splitting of the 22GHz H2O masers toward NGC7538-IRS1. The European VLBI Network and the MERLIN telescopes were used to measure the linear polarization and the Zeeman-splitting of the 6.7GHz CH3OH masers toward the same region. We detected 17 H2O masers and 49 CH3OH masers at high angular resolution. We detected linear polarization emission toward two H2O masers and toward twenty CH3OH masers. The CH3OH masers, most of which only show a core structure, seem to trace rotating and potentially infalling gas in the inner part of a torus. Significant Zeeman-splitting was measured in three CH3OH masers. [...] We also propose a new description of the structure of the NGC7538-IRS1 maser region.

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