AN ORDERED MAGNETIC FIELD IN THE PROTOPLANETARY DISK OF AB Aur REVEALED BY MID-INFRARED POLARIMETRY
AN ORDERED MAGNETIC FIELD IN THE PROTOPLANETARY DISK OF AB Aur REVEALED BY MID-INFRARED POLARIMETRY
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中红外偏振测量揭示AB Aur原行星盘中的有序磁场
DOI：
10.3847/0004-637x/832/1/18
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
N. Marinas
中科院分区：
文献类型：
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作者：
Dan Li;E. Pantin;C. Telesco;Han Zhang;C. Wright;P. Barnes;C. Packham;N. Marinas
磁场（B 场）在原行星盘的形成和演化中发挥着关键作用，但由于缺乏观测限制，人们对其特性知之甚少。使用 10.4 m Gran Telescopio Canarias 的 CanariCam，我们绘制了 Herbig Ae 星 AB Aur 周围原行星盘的中红外偏振图。我们在 AB Aur 内盘 (r < 80 au) 的 10.3 μm 处检测到 ∼0.44% 极化，在较大半径处上升到 ∼1.4%。我们的模拟表明，内盘的中红外偏振源自盘 B 场中排列的细长粒子的二向色发射。该场在空间尺度上有序排列，与我们的分辨率（∼50 au）相称，并且我们推断出一个从圆盘的旋转轴倾斜的极向形状。 AB Aur 圆盘的光学厚度为 10.3 μm，因此该波长的偏振测量正在探测圆盘表面附近的 B 场。因此，我们的观察证实，这一层确实很可能被磁化，这一层受到一些发展磁旋转不稳定性及其由此产生的粘度的理论研究的青睐。在超过~80 au的半径处，中红外偏振主要是由尺寸高达~1μm的尘埃颗粒的散射引起的，该尺寸表明颗粒生长，并且可能表明颗粒从圆盘中平面的湍流放样。
Magnetic fields (B-fields) play a key role in the formation and evolution of protoplanetary disks, but their properties are poorly understood due to the lack of observational constraints. Using CanariCam at the 10.4 m Gran Telescopio Canarias, we have mapped out the mid-infrared polarization of the protoplanetary disk around the Herbig Ae star AB Aur. We detect ∼0.44% polarization at 10.3 μm from AB Aur's inner disk (r < 80 au), rising to ∼1.4% at larger radii. Our simulations imply that the mid-infrared polarization of the inner disk arises from dichroic emission of elongated particles aligned in a disk B-field. The field is well ordered on a spatial scale, commensurate with our resolution (∼50 au), and we infer a poloidal shape tilted from the rotational axis of the disk. The disk of AB Aur is optically thick at 10.3 μm, so polarimetry at this wavelength is probing the B-field near the disk surface. Our observations therefore confirm that this layer, favored by some theoretical studies for developing magneto-rotational instability and its resultant viscosity, is indeed very likely to be magnetized. At radii beyond ∼80 au, the mid-infrared polarization results primarily from scattering by dust grains with sizes up to ∼1 μm, a size indicating both grain growth and, probably, turbulent lofting of the particles from the disk mid-plane.