STRINGENT LIMITS ON THE POLARIZED SUBMILLIMETER EMISSION FROM PROTOPLANETARY DISKS
STRINGENT LIMITS ON THE POLARIZED SUBMILLIMETER EMISSION FROM PROTOPLANETARY DISKS
复制标题
原行星盘偏振亚毫米级发射的严格限制
DOI：
10.1088/0004-637x/704/2/1204
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
R. Rao
中科院分区：
文献类型：
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作者：
A. Hughes;D. Wilner;Jungyeon Cho;D. Marrone;A. Lazarian;S. Andrews;R. Rao
本文利用弧秒分辨率的亚毫米波阵列（SMA）偏振观测，对两颗邻近恒星hd163296和长蛇座TW的原行星盘发出的880 μm连续辐射进行了观测。虽然以前的观测和理论工作表明，这种圆盘的毫米连续发射通常有2%-3%的极化率，但我们在每个弧秒尺度光束中没有检测到超过3σ上限（7 mJy）的极化连续发射，或者在集成连续发射中发现小于1%的极化连续发射。我们将SMA上限与探索性Cho & Lazarian模型的预测结果进行了比较，该模型预测了金牛座T盘在环向磁场作用下的极化发射，并在~ 10σ水平上排除了他们的基准模型。我们探讨了造成这种差异的一些潜在原因，重点是描述磁盘中颗粒形状、磁场排列和尺寸分布的模型参数。我们还研究了相关的影响，如磁场强度和几何形状、大晶粒的散射和晶粒排列效率，包括在基准模型中未考虑的晶粒排列理论的最新进展。我们讨论了每个参数对数据的影响，并确定极化发射的抑制可能是由大晶粒的圆角、晶粒与磁场对齐效率的降低和/或某种程度的磁场缠结（可能是由于湍流）引起的。极向磁场的几何形状也可以减少极化信号，特别是对于像TW Hya圆盘这样的正面观察几何形状。这里提供的数据提供了迄今为止对年轻恒星周围的圆盘偏振毫米波长辐射的最严格限制。
We present arcsecond-resolution Submillimeter Array (SMA) polarimetric observations of the 880 μm continuum emission from the protoplanetary disks around two nearby stars, HD 163296 and TW Hydrae. Although previous observations and theoretical work have suggested that a 2%–3% polarization fraction should be common for the millimeter continuum emission from such disks, we detect no polarized continuum emission above a 3σ upper limit of 7 mJy in each arcsecond-scale beam, or <1% in integrated continuum emission. We compare the SMA upper limits with the predictions from the exploratory Cho & Lazarian model of polarized emission from T Tauri disks threaded by toroidal magnetic fields, and rule out their fiducial model at the ∼10σ level. We explore some potential causes for this discrepancy, focusing on model parameters that describe the shape, magnetic field alignment, and size distribution of grains in the disk. We also investigate related effects like the magnetic field strength and geometry, scattering off of large grains, and the efficiency of grain alignment, including recent advances in grain alignment theory, which are not considered in the fiducial model. We discuss the impact each parameter would have on the data and determine that the suppression of polarized emission plausibly arises from rounding of large grains, reduced efficiency of grain alignment with the magnetic field, and/or some degree of magnetic field tangling (perhaps due to turbulence). A poloidal magnetic field geometry could also reduce the polarization signal, particularly for a face-on viewing geometry like the TW Hya disk. The data provided here offer the most stringent limits to-date on the polarized millimeter-wavelength emission from disks around young stars.