行星状星云K3-35中6 GHz OH脉泽的VLBI观测研究

Planetary Nebulae (PNe) are objects created during the final stage of the life of low- or intermediate-mass stars, which are meaningful for studying the late evolution of stars. The bright and compact maser emission in PN is the ideal target for high resolution VLBI observations. Studying the spatial distribution, kinematics and magnetic field traced by masers in PN with VLBI observations can help us understand how an evolved star goes through the AGB phase to the PN phase. K3-35 is a very young PN, which is the brighter one of two PNe currently detected 6 GHz OH masers. Since the VLBI observations of 6 GHz OH masers toward PNe are scarce at present, we propose a research project which planning to carry out multi-epoch VLBI polarized observations on 6 GHz OH masers in K3-35 with the European VLBI Network (EVN), to reveal the spatial distribution, kinematics and magnetic field traced by this kind of masers. The results will help us understand how the bipolar shape of K3-35 forms. By Carrying out this project we will obtain the polarization VLBI images of 6 GHz OH masers in PN with the spatial resolution of milli-arcsecond level for the first time, and may give some useful experience for more and more similar studies in future.

行星状星云（Planetary Nebula，PN）是中小质量恒星演化到晚期的一种产物，对于研究恒星的晚期演化行为很有意义。PN中亮而致密的脉泽辐射是高分辨率VLBI观测的理想目标，利用VLBI手段开展PN中脉泽辐射斑的分布、运动学和磁场研究有助于理解晚型星从AGB阶段向PN阶段渐次演化的过程。K3-35是一个非常年轻的PN，是目前探测到6 GHz 羟基脉泽的两个行星状星云中辐射较强的一个。目前对PN中6 GHz羟基脉泽的VLBI观测研究非常稀少，而我们所申请的研究项目，计划利用欧洲VLBI网（EVN）对K3-35中6 GHz羟基脉泽开展多历元VLBI偏振观测研究，揭示其空间分布形态、运动学及磁场特征，这将有助于理解该星云bipolar形态的形成过程。该项目的实施将在毫角秒分辨率上首次获得PN中6 GHz羟基脉泽的偏振图像，并有可能为今后更多的6 GHz羟基脉泽的VLBI观测研究提供参考。

我们利用欧洲VLBI网对行星状星云K3-35中6 GHz OH脉泽进行了高分辨率观测研究，以研究行星状星云中6 GHz OH脉泽辐射区的高分辨率形态、空间分布以及其示踪的磁场性质。利用欧洲VLBI网的总功率和偏振观测数据，我们首次得到了行星状星云中6 GHz OH脉泽的毫角秒分辨率图像，并利用塞曼分裂效应得到了该脉泽示踪的径向磁场强度为3.5 mG，符合晚型星的磁场模型，推测激发态的6 GHz OH脉泽辐射区比1.6 GHz OH脉泽更靠近行星状星云内部。这些结果显示，行星状星云中的6 GHz OH脉泽在毫角秒尺度下依然很致密，在高分辨率的VLBI观测中可以探测到较高精度的脉泽辐射塞曼分裂精细结构，可以是研究行星状星云运动学、磁场和抽运环境的很好的示踪器。此外，在该项目资助下，我们还开展了其他相关研究工作并取得了部分研究成果。