Parkes observations for project P1219 semester 2023OCTS_20

The magnetic field potentially regulates the process of star formation and the evolution of molecular clouds. It is inherently difficult to measure interstellar magnetic field strengths, with the measurement of Zeeman splitting a unique method to estimate the magnetic field strength along the line of sight directly. Despite the detection of Zeeman splitting in other mediums, there are as yet no Zeeman detections against compact background sources in quiescent molecular clouds or the cold neutral medium. Pulsars with extremely small solid angles and relatively high transverse velocities are ideal background sources to study the magnetic field in molecular clouds, providing a distinct signal to measure splitting against. There are four pulsars with OH absorption detections, namely PSR B1849+00, B1641-45, B1718-35, and B1749-28. We propose to utilize these four pulsars to explore the properties of the magnetic field and its variations within molecular clouds through both the Zeeman splitting of OH absorption and rotation measure estimations, between epochs. If a detection is confirmed, it will open a new window on the hard-to-measure magnetic fields in molecular clouds, independent of interpretation, thus shedding light on the physics of star formation and the interstellar medium.

磁场可调控恒星形成过程与分子云的演化。直接测量星际磁场（interstellar magnetic field）强度本质上极具挑战性，而塞曼分裂（Zeeman splitting）是唯一可直接估算视线方向磁场强度的方法。尽管已在其他介质中探测到塞曼分裂，但目前尚无在宁静分子云或冷中性介质中针对致密背景源的塞曼分裂探测报道。具有极小张角与相对较高横向速度的脉冲星，是研究分子云磁场的理想背景源，可提供清晰的分裂信号以供测量。目前已发现4颗存在OH吸收探测的脉冲星，分别为PSR B1849+00、B1641-45、B1718-35与B1749-28。我们提议利用这4颗脉冲星，通过不同观测时段下的OH吸收塞曼分裂与旋转量（rotation measure）估算，探究分子云内的磁场特性及其变化规律。若能成功确认探测信号，将为难以观测的分子云磁场研究打开全新窗口，且不受特定解释框架的限制，从而为恒星形成与星际介质（interstellar medium）的物理机制研究提供新的认知。