Barnard 68的磁场畸变
Distortion of Magnetic Fields in Barnard 68
摘要：
通过对背景星的近红外偏振观测，测量了无星致密核Barnard 68（B68）中尘埃颗粒排列产生的二向色偏振光，揭示了该核的磁场结构、运动学稳定性和演化状态.减去无关的环境极化分量后，遍布B68的磁场映射使用38颗恒星和轴对称扭曲沙漏状磁场得到，虽然证据沙漏场不是很强。在简单的二维和三维磁场建模的基础上，确定了在天空平面和视线方向上的磁倾角分别为$47^{\circ} \pm 5^{\circ}$和$20^{\circ} \pm 10^{\circ}$。得到B68的总磁场强度为$26.1 \pm 8.7$ $μ{\rm G}$。使用磁性和热/湍流支持评估的B68的临界质量是$M_{\rm cr} = 2.30 \pm 0.20$ ${\rm M}_{\odot}$，这与观测到的$M_{\rm core}=2.1$ M $_{\odot}$的核心质量一致，表明接近临界状态。我们发现，在$A_V \sim 30$ mag以下，对最深遮蔽的恒星，偏振和消光之间存在相对线性的关系。需要进一步的理论和观测研究来解释核心寒冷和密集区域的尘埃排列。
英文摘要：
The magnetic field structure, kinematical stability, and evolutionary status of the starless dense core Barnard 68 (B68) are revealed based on the near-infrared polarimetric observations of background stars, measuring the dichroically polarized light produced by aligned dust grains in the core. After subtracting unrelated ambient polarization components, the magnetic fields pervading B68 are mapped using 38 stars and axisymmetrically distorted hourglass-like magnetic fields are obtained, although the evidence for the hourglass field is not very strong. On the basis of simple 2D and 3D magnetic field modeling, the magnetic inclination angles on the plane-of-sky and in the line-of-sight direction are determined to be $47^{\circ} \pm 5^{\circ}$ and $20^{\circ} \pm 10^{\circ}$, respectively. The total magnetic field strength of B68 is obtained to be $26.1 \pm 8.7$ $μ{\rm G}$. The critical mass of B68, evaluated using both magnetic and thermal/turbulent support, is $M_{\rm cr} = 2.30 \pm 0.20$ ${\rm M}_{\odot}$, which is consistent with the observed core mass of $M_{\rm core}=2.1$ M$_{\odot}$, suggesting nearly critical state. We found a relatively linear relationship between polarization and extinction up to $A_V \sim 30$ mag toward the stars with deepest obscuration. Further theoretical and observational studies are required to explain the dust alignment in cold and dense regions in the core.
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