A wind-driving disc model for the mm-wavelength polarization structure of HL Tau
A wind-driving disc model for the mm-wavelength polarization structure of HL Tau
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DOI：
10.1093/mnras/stw2175
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发表时间：
2016-08
影响因子：
4.8
通讯作者：
T. Matsakos;P. Tzeferacos;A. Konigl
中科院分区：
文献类型：
--
作者：
T. Matsakos;P. Tzeferacos;A. Konigl
最近在原恒星吸积盘中出现的空间分辨毫米波和厘米波偏振测量技术可以帮助阐明磁场在这些系统中角动量传输中的作用。迄今为止最好的情况是 HL~Tau，其中无法通过垂直和方位角磁场分量的组合产生与 1.25 毫米数据的良好拟合，这被解释为暗示离心驱动风 (CDW) 可能不是观测探测到的 $\sim 10^2\,$au 尺度上的重要传输机制。使用启发式单场分量圆盘的合成偏振图和风驱动圆盘的后处理模拟，我们证明，如果径向场分量（CDW 机制的标志）在偏振发射区域占主导地位，则可以获得更好的数据拟合。之前在对银河系中心 PC 级尘埃环的远红外偏振图进行建模时也做出了类似的推论。为了使这种解释与原恒星盘的理论模型相一致，原恒星盘的理论模型表明风是从中平面以上相对较高的高度发射的，我们提出，大部分偏振发射源自于保持悬浮在中平面上方的小颗粒($\la 0.1\,$mm)，具有高($\ga 10$\%)内在偏振度，而大部分毫米波长发射是由较大的颗粒产生的，具有低内在偏振，已经稳定到中位面。
The recent advent of spatially resolved mm- and cm-wavelength polarimetry in protostellar accretion discs could help clarify the role of magnetic fields in the angular momentum transport in these systems. The best case to date is that of HL~Tau, where the inability to produce a good fit to the 1.25-mm data with a combination of vertical and azimuthal magnetic field components was interpreted as implying that centrifugally driven winds (CDWs) are probably not a significant transport mechanism on the $\sim 10^2\,$au scale probed by the observations. Using synthetic polarization maps of heuristic single-field-component discs and of a post-processed simulation of a wind-driving disc, we demonstrate that a much better fit to the data can be obtained if the radial field component, a hallmark of the CDW mechanism, dominates in the polarized emission region. A similar inference was previously made in modelling the far-infrared polarization map of the pc-scale dust ring in the Galactic centre. To reconcile this interpretation with theoretical models of protostellar discs, which indicate that the wind is launched from a comparatively high elevation above the mid-plane, we propose that most of the polarized emission originates -- with a high ($\ga 10$\%) intrinsic degree of polarization -- in small ($\la 0.1\,$mm) grains that remain suspended above the mid-plane, and that the bulk of the mm-wavelength emission is produced -- with low intrinsic polarization -- by larger grains that have settled to the mid-plane.