Vlemmings Wouter H T, Diamond Philip J, Imai Hiroshi
Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire SK11 9DL, UK.
Nature. 2006 Mar 2;440(7080):58-60. doi: 10.1038/nature04466.
Planetary nebulae often have asymmetric shapes, even though their progenitor stars were symmetric; this structure could be the result of collimated jets from the evolved stars before they enter the planetary nebula phase. Theoretical models have shown that magnetic fields could be the dominant source of jet-collimation in evolved stars, just as these fields are thought to collimate outflows in other astrophysical sources, such as active galactic nuclei and proto-stars. But hitherto there have been no direct observations of both the magnetic field direction and strength in any collimated jet. Here we report measurements of the polarization of water vapour masers that trace the precessing jet emanating from the asymptotic giant branch star W43A (at a distance of 2.6 kpc from the Sun), which is undergoing rapid evolution into a planetary nebula. The masers occur in two clusters at opposing tips of the jets, approximately 1,000 au from the star. We conclude from the data that the magnetic field is indeed collimating the jet.
行星状星云通常具有不对称的形状，尽管其前身恒星是对称的；这种结构可能是恒星在进入行星状星云阶段之前由准直喷流造成的。理论模型表明，磁场可能是演化恒星中喷流准直的主要来源，就像这些磁场被认为在其他天体物理源（如活动星系核和原恒星）中准直外流一样。但迄今为止，尚未对任何准直喷流中的磁场方向和强度进行过直接观测。在此，我们报告了对水蒸气脉泽偏振的测量结果，这些脉泽追踪了渐近巨星分支恒星W43A（距离太阳2.6千秒差距）发出的进动喷流，该恒星正在迅速演化为行星状星云。脉泽出现在喷流相对两端的两个星团中，距离恒星约1000天文单位。我们从数据中得出结论，磁场确实在使喷流准直。
