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arXiv 2008.04952astro-ph.SRastro-ph.GA
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HD 142527和IM Lup两颗原行星盘中的低水平一氧化碳线极化

Low Level Carbon Monoxide Line Polarization in two Protoplanetary Disks: HD 142527 and IM Lup

Ian W. Stephens, Manuel Fernandez-Lopez, Zhi-Yun Li, Leslie W. Looney, Richard Teague

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Accepted to ApJ
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摘要：

磁场预计将在星周盘的吸积过程中发挥重要作用。测量磁场形态是困难的，特别是因为偏振（亚）毫米连续观测可能无法跟踪在大多数磁盘的字段。Goldreich-Kylafis（GK）效应表明线极化垂直或平行于磁场方向。我们试图观测到CO（2-1）、$^{13}$ CO（2-1）和C $^{18}$ O（2-1）线向HD 142527和IM Lup的偏振，它们是大而明亮的原行星盘。我们使用空间平均和光谱积分搜索信号在两个磁盘，并检测到一个潜在的CO（2-1）斯托克斯$Q$信号向两个磁盘。HD 142527和IM Lup的总CO（2-1）极化分数分别为1.57 $\pm$ 0.18%和1.01 $\pm$ 0.10%。我们的蒙特卡罗模拟表明，这些信号是边际。我们也堆叠斯托克斯参数的基础上开普勒旋转，但没有信号被发现。在整个磁盘跟踪的尘埃HD 142527，3 PDMATHAMBMQ上限为$P_{\text{frac}}$在0.5 $^{\prime\prime}$（$\sim$ 80 au）分辨率通常小于3%的CO（2-1）和$^{13}$ CO（2- 1）和4%的C $^{18}$ O（2-1）。对于IM Lup，这三条线的3个$σ$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$\sim$ 10倍，尽管堆叠区域可以潜在地平均小尺度偏振结构。我们还比较了我们的连续偏振在1.3毫米观测在870 $μ$米从以前的研究。在HD 142527的北部尘埃陷阱的偏振显示了显着的变化形态和增加$P_{\text{frac}}$相比，870 $μ$米。对于IM Lup，1.3 mm偏振可能更具有方位角，并且具有比870 $μ$ m处更高的$P_{\text{frac}}$。

英文摘要：

Magnetic fields are expected to play an important role in accretion processes for circumstellar disks. Measuring the magnetic field morphology is difficult, especially since polarimetric (sub)millimeter continuum observations may not trace fields in most disks. The Goldreich-Kylafis (GK) effect suggests that line polarization is perpendicular or parallel to the magnetic field direction. We attempt to observe CO(2-1), $^{13}$CO(2-1), and C$^{18}$O(2-1) line polarization toward HD 142527 and IM Lup, which are large, bright protoplanetary disks. We use spatial averaging and spectral integration to search for signals in both disks, and detect a potential CO(2-1) Stokes $Q$ signal toward both disks. The total CO(2-1) polarization fractions are 1.57 $\pm$ 0.18% and 1.01 $\pm$ 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 3$σ$ upper limits for $P_{\text{frac}}$ at 0.5$^{\prime\prime}$ ($\sim$80 au) resolution are typically less than 3% for CO(2-1) and $^{13}$CO(2-1) and 4% for C$^{18}$O(2-1). For IM Lup, the 3$σ$ 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 $\sim$10 lower, though stacking areas can potentially average out small-scale polarization structure. We also compare our continuum polarization at 1.3 mm to observations at 870 $μ$m from previous studies. The polarization in the northern dust trap of HD 142527 shows a significant change in morphology and an increase in $P_{\text{frac}}$ as compared to 870 $μ$m. For IM Lup, the 1.3 mm polarization may be more azimuthal and has a higher $P_{\text{frac}}$ than at 870 $μ$m.

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