Low-level Carbon Monoxide Line Polarization in Two Protoplanetary Disks: HD 142527 and IM Lup
Low-level Carbon Monoxide Line Polarization in Two Protoplanetary Disks: HD 142527 and IM Lup
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DOI：
10.3847/1538-4357/abaef7
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发表时间：
2020-08
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影响因子：
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通讯作者：
I. Stephens;M. Fernández-López;Zhi-Yun Li;L. Looney;R. Teague
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作者：
I. Stephens;M. Fernández-López;Zhi-Yun Li;L. Looney;R. Teague
磁场在星周盘的吸积过程中起着重要的作用。然而，测量磁场形态是困难的，特别是当极化（亚）毫米连续观测可能无法跟踪大多数磁盘中的字段。Goldreich-Kylafis效应表明线极化垂直或平行于磁场方向。我们试图观测CO（2−1）、13 CO（2−1）和C18 O（2−1）的线偏振，它们指向HD 142527和IM Lup，这两个盘是大而明亮的原行星盘。我们使用空间平均和光谱积分来搜索两个圆盘中的信号，并且我们检测到朝向两个圆盘的潜在CO（2−1）Stokes Q信号。HD 142527和IM Lup的总CO（2−1）极化分数分别为1.57% ± 0.18%和1.01% ± 0.10%。我们的蒙特卡罗模拟表明，这些信号是边际。在HD 142527的尘埃盘上，在05（Au）分辨率下，CO（2−1）和13 CO（2− 1）的3σ上限通常小于3%，C18 O（2 − 1）的3σ上限通常小于4%。对于IM Lup，这三条线的3σ上限通常分别小于3%、4%和12%。基于我们的堆叠技术的上限最多低1000倍，尽管堆叠区域可能会使小尺度偏振结构平均化。我们还比较了我们在1.3 mm处的连续偏振与以前研究中在870 μm处的观测结果。在HD 142527的北方尘埃阱中，偏振显示出与870 μm相比在形态上的显著变化和增加。对于IM Lup，1.3 mm偏振可能更具有方位角，并且具有比870 μm处更高的a。
Magnetic fields are expected to play an important role in accretion processes for circumstellar disks. However, measuring the magnetic field morphology is difficult, especially when given that polarimetric (sub)millimeter continuum observations may not trace the fields in most disks. The Goldreich–Kylafis effect suggests that line polarization is perpendicular or parallel to the magnetic field direction. We attempt to observe CO(2−1), 13CO(2−1), and C18O(2−1) line polarization toward HD 142527 and IM Lup, which are large and bright protoplanetary disks. We use spatial averaging and spectral integration to search for signals in both disks, and we detect a potential CO(2−1) Stokes Q signal toward both disks. The total CO(2−1) polarization fractions are 1.57% ± 0.18% and 1.01% ± 0.10% for HD 142527 and IM Lup, respectively. Our Monte Carlo simulations indicate that these signals are marginal. We also stack Stokes parameters based on the Keplerian rotation, but no signal was found. Across the disk traced by dust of HD 142527, the 3σ upper limits for at 05 (∼80 au) resolution are typically less than 3% for CO(2−1) and 13CO(2−1) and 4% for C18O(2−1). For IM Lup the 3σ upper limits for these three lines are typically less than 3%, 4%, and 12%, respectively. Upper limits based on our stacking technique are up to a factor of ∼10 lower, although stacking areas can potentially average out small-scale polarization structure. We also compare our continuum polarization at 1.3 mm to observations at 870 μm from previous studies. The polarization in the northern dust trap of HD 142527 shows a significant change in morphology and an increase in as compared to 870 μm. For IM Lup, the 1.3 mm polarization may be more azimuthal and has a higher than at 870 μm.