在IRAM 30米望远镜上用XPOL观测恒星形成区的Goldreich-Kylafis效应
Observations of the Goldreich-Kylafis effect in star-forming regions with XPOL at the IRAM 30m telescope
摘要：
Goldreich-Kylafis（GK）效应导致某些分子线发射被弱线性偏振，例如，在存在磁场的情况下。与偏振尘埃辐射相比，GK效应有可能通过其对线轮廓中的速度的依赖而产生沿视线的额外信息。我们的目标是检测偏振分子线发射朝向DR 21（OH），W3 OH/H2O，G34.3+0.2，和UYSO 1密集的分子云核心的稀有CO同位素和CS的过渡。这种观测的可行性必须通过研究极化旁瓣的影响来确定，在密集源周围存在扩展发射的情况下。观测是用IRAM 30米望远镜进行的，使用了相关偏振计XPOL和两个正交偏振接收器。我们制作了光束图来研究仪器偏振。虽然在几乎所有的过渡到所有的来源极化的信号被发现，其程度的极化只有在一种情况下超过极化，可以预期由于仪器的影响。结果表明，即使源是非极化的，系统极化旁瓣中的任何辐射都能产生仪器极化。在朝向G34.3+0.2的CS（2-1）线中发现了pL<~1.5%的天文偏振线发射的初步证据。
英文摘要：
The Goldreich-Kylafis (GK) effect causes certain molecular line emission to be weakly linearly polarized, e.g., in the presence of a magnetic field. Compared to polarized dust emission, the GK effect has the potential to yield additional information along the line of sight through its dependence on velocity in the line profile. Our goal was to detect polarized molecular line emission toward the DR21(OH), W3OH/H2O, G34.3+0.2, and UYSO1 dense molecular cloud cores in transitions of rare CO isotopologues and CS. The feasibility of such observations had to be established by studying the influence of polarized sidelobes, e.g., in the presence of extended emission in the surroundings of compact sources. The observations were carried out with the IRAM 30m telescope employing the correlation polarimeter XPOL and using two orthogonally polarized receivers. We produced beam maps to investigate instrumental polarization. While in nearly all transitions toward all sources a polarized signal is found, its degree of polarization only in one case surpasses the polarization that can be expected due to instrumental effects. It is shown that any emission in the polarized sidelobes of the system can produce instrumental polarization, even if the source is unpolarized. Tentative evidence for astronomically polarized line emission with pL<~1.5% was found in the CS(2-1) line toward G34.3+0.2.
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