EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions
EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions
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DOI：
10.1051/0004-6361/201321501
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发表时间：
2013-06
期刊：
影响因子：
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通讯作者：
G. Surcis;W. Vlemmings;H. V. Langevelde;B. H. Kramer;Luis Henry Quiroga-Nuñez
中科院分区：
文献类型：
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作者：
G. Surcis;W. Vlemmings;H. V. Langevelde;B. H. Kramer;Luis Henry Quiroga-Nuñez
上下文直到最近，磁场才被纳入大质量星星形成的理论模拟中。模拟结果表明，磁场在分子外流的形成和动力学过程中起着重要的作用。微波激射器，特别是6.7-GHz CH 3OH微波激射器，是在10-100 Au最小尺度上研究大质量年轻恒星周围磁场形态的最佳探测器。目标。利用6.7-GHz CH_3OH脉泽辐射提供大质量年轻恒星周围磁场形态的新观测测量结果，对于大质量星星形成的数值模拟设定约束条件是非常重要的。方法.本文重点关注4个大质量年轻恒星天体，IRAS 06058+2138-NIRS 1，IRAS 22272+ 6358 A，S255-IR和S231，它们补充了我们之前的2012年样本（第一个EVN群）。从所有这些来源，分子外流已被检测到在过去。七个欧洲VLBI网络的天线被用来测量的线性偏振和塞曼分裂的6.7-GHz的CH 3OH脉泽在恒星形成的地区，在这第二个EVN组。结果我们总共探测到128个CH 3OH脉泽云。在我们的样品中，18%的CH_3OH脉泽被检测到分数线偏振（0.8%-11.3%）。在所有的大质量年轻星体中，线偏振矢量都是有序的。我们在IRAS 06058+2138-NIRS 1和S255-IR中测量到显著的塞曼分裂（Δ VZ = 3.8 ± 0.6 m s-1和ΔVZ = 3.2 ± 0.7 m s-1）。结论.通过对20个大质量年轻天体的观测，我们发现在两半球的6.7GHz CH_3OH脉泽的线性分布与外流或线性偏振矢量之间没有明显的相关性。另一方面，我们提出的第一个统计证据表明，磁场（规模10-100 Au）主要是定向沿着大规模的外流方向。此外，我们还通过实验发现，不饱和CH 3OH脉泽的线偏振分数Pl <4.5%。© ESO，2013.
Context. Magnetic fields have only recently been included in theoretical simulations of high-mass star formation. The simulations show that magnetic fields play an important role in the formation and dynamics of molecular outflows. Masers, in particular 6.7-GHz CH3OH masers, are the best probes of the magnetic field morphologies around massive young stellar objects on the smallest scales of 10-100 AU. Aims. Providing new observational measurements of the morphology of magnetic fields around massive young stellar objects by using 6.7-GHz CH3OH maser emission is very important for setting constraints on the numerical simulations of massive star formation. Methods. This paper focuses on 4 massive young stellar objects, IRAS 06058+2138-NIRS 1, IRAS 22272+6358A, S255-IR, and S231, which complement our previous 2012 sample (the first EVN group). From all these sources, molecular outflows have been detected in the past. Seven of the European VLBI Network antennas were used to measure the linear polarization and Zeeman-splitting of the 6.7-GHz CH3OH masers in the star-forming regions in this second EVN group. Results. We detected a total of 128 CH3OH masing cloudlets. Fractional linear polarization (0.8%-11.3%) was detected towards 18% of the CH3OH masers in our sample. The linear polarization vectors are well ordered in all the massive young stellar objects. We measured significant Zeeman-splitting in IRAS 06058+2138-NIRS 1 (ΔVZ = 3.8 ± 0.6 m s-1) and S255-IR (ΔVZ = 3.2 ± 0.7 m s-1). Conclusions. By considering the 20 massive young stellar objects towards which the morphology of magnetic fields was determined by observing 6.7-GHz CH3OH masers in both hemispheres, we find no evident correlation between the linear distributions of CH3OH masers and the outflows or the linear polarization vectors. On the other hand, we present first statistical evidence that the magnetic field (on scales 10-100 AU) is primarily oriented along the large-scale outflow direction. Moreover, we empirically find that the linear polarization fraction of unsaturated CH 3OH masers is Pl < 4.5%. © ESO, 2013.