用SOFIA/HAWC +约束博克球B335的磁场性质
Constraining the magnetic field properties of Bok globule B335 using SOFIA/HAWC+
摘要：
由于它们定义明确的形状和大多数孤立的位置，博克球状体是研究低质量恒星形成物理学的合适对象。为了研究原型博克球B335的磁场，我们用SOFIA/HAWC+在214 $\,μ$ m波长处获得了空间分辨的偏振图。这些观测首次揭示了博克球中的偏振空穴，即朝向其致密中心的偏振度减小，也发生在远红外波长区域。所观察到的偏振模式是均匀的，平均偏振角为48 $^\circ\pm $ 26 $^\circ$，磁场强度为$\sim$ 142 $\,μ$ G。此外，我们使用互补的极化数据B335在近红外毫米波长的分析和约束的磁场跨越不同的尺度。通过应用3D Monte-Carlo辐射传输代码POLARIS（Reissl等人，2016），我们开发了一个用于该球状体的密度和磁场结构以及尘埃特性的模型。我们得出结论，B335中心的柱密度太低，无法通过二向色吸收在B335中产生观察到的偏振孔（Brauer等人，2016）。此外，我们得出结论，自散射的效果没有显着的影响所观察到的偏振。通过辐射力矩机制采用尘埃颗粒排列，星际辐射场和中央恒星作为辐射源的组合与B335外部区域（距离核心$\approx\,$ 10 $^4\,$ au）偏振度的降低一致。然而，该模型未能解释内5000 au的低偏振度。
英文摘要：
Thanks to their well-defined shape and mostly isolated locations, Bok globules are suitable objects for studying the physics of low-mass star formation. To study the magnetic field of the prototypical Bok globule B335, we obtained a spatially resolved polarization map with SOFIA/HAWC+ at a wavelength of 214$\,μ$m. For the first time, these observations reveal that polarization holes in Bok globules, that is, the decrease in polarization degree towards their dense centers, also occur in the far-infrared wavelength regime. The observed polarization pattern is uniform with a mean polarization angle of 48$^\circ\pm $26$^\circ$ and a magnetic field strength of $\sim$ 142$\,μ$G. Moreover, we use complementary polarimetic data for B335 obtained at near-infrared to millimeter wavelengths to analyze and constrain the magnetic field across different scales. By applying the 3D Monte-Carlo radiative transfer code POLARIS (Reissl et al. 2016), we developed a model for the density and magnetic field structure as well as for the dust properties of this globule. We conclude that the column density towards the center of B335 is too low to cause the observed polarization hole in B335 via dichroic absorption (Brauer et al. 2016). Furthermore, we conclude that the effect of self-scattering has no significant impact on the observed polarization. Adopting dust-grain alignment via the radiative torque mechanism, a combination of the interstellar radiation field and the central star as radiation sources is consistent with the decrease in polarization degree at the outer regions of B335 ($\approx\,$10$^4\,$au from the core). However, the model fails to explain the low polarization degree within the inner 5000 au.
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