Highly Ordered and Pinched Magnetic Fields in the Class 0 Protobinary System L1448 IRS 2
Highly Ordered and Pinched Magnetic Fields in the Class 0 Protobinary System L1448 IRS 2
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DOI：
10.3847/1538-4357/ab24c8
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发表时间：
2018-05
期刊：
影响因子：
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通讯作者：
W. Kwon;I. Stephens;J. Tobin;L. Looney;Zhi-Yun Li;F. V. D. van der Tak;R. Crutcher
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文献类型：
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作者：
W. Kwon;I. Stephens;J. Tobin;L. Looney;Zhi-Yun Li;F. V. D. van der Tak;R. Crutcher
我们使用阿塔卡马大型毫米/亚毫米阵列对0级原恒星系统L1448 IRS 2进行了偏振观测，该系统是嵌入在扁平旋转结构中的原双星，并且暗示其存在中心圆盘，但其磁场与云核尺度上的双极流出一致。我们的高灵敏度和高分辨率（~100 au）观测显示出以原恒星系统为中心的清晰沙漏磁场形态，但中心模式与表明星周盘的环形场一致；不过，其他解释也是可能的，包括由赤道吸积流拖曳成平行于中平面的配置的场线。如果确实存在相对较大的圆盘，则表明该系统中避免了磁制动灾难，不是通过磁轴和旋转轴之间的较大失准，而是通过一些其他机制，例如非理想磁流体动力学效应和/或湍流。我们还发现了极化分数随强度减小的关系，并且这种关系的各种斜率可以理解为多种极化机制和/或来自变化的场形态的去极化。此外，我们发现了一个突出的块状去极化带穿过垂直于双极流出的中心。此外，对磁场强度的粗略估计表明，磁场强度足以阻碍旋转支撑盘的形成，这与中心环形场的特征不一致。这也表明，即使在具有强大原始磁场的年轻恒星中，早期盘的形成也可能发生。
We have carried out polarimetric observations with the Atacama Large Millimeter/submillimeter Array toward the Class 0 protostellar system L1448 IRS 2, which is a protobinary embedded within a flattened, rotating structure, and for which a hint of a central disk has been suggested, but whose magnetic fields are aligned with the bipolar outflow on the cloud core scale. Our high-sensitivity and high-resolution (∼100 au) observations show a clear hourglass magnetic field morphology centered on the protostellar system, but the central pattern is consistent with a toroidal field indicative of a circumstellar disk; though, other interpretations are also possible, including field lines dragged by an equatorial accretion flow into a configuration parallel to the midplane. If a relatively large disk does exist, it would suggest that the magnetic braking catastrophe is averted in this system, not through a large misalignment between the magnetic and rotation axes, but rather through some other mechanisms, such as nonideal magnetohydrodynamic effects and/or turbulence. We have also found a relationship of decreasing polarization fractions with intensities and the various slopes of this relationship can be understood as multiple polarization mechanisms and/or depolarization from a changing field morphology. In addition, we found a prominent clumpy depolarization strip crossing the center perpendicular to the bipolar outflow. Moreover, a rough estimate of the magnetic field strength indicates that the field is strong enough to hinder formation of a rotationally supported disk, which is inconsistent with the feature of a central toroidal field. This also suggests that early disk formation can happen even in young stellar objects with a strong primordial magnetic field.