Parkes observations for project P1219 semester 2023OCTS_11

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。星际磁场强度的测量本就极具挑战，而塞曼分裂（Zeeman splitting）是目前唯一可直接沿视线方向估算磁场强度的方法。尽管已在其他介质中探测到塞曼分裂，但截至目前，尚未在宁静分子云或冷中性介质（cold neutral medium）中的致密背景源处发现塞曼探测信号。
具有极小立体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，可提供清晰的分裂探测参照信号。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及B1749-28。
我们计划利用这4颗脉冲星，通过OH吸收的塞曼分裂以及不同观测历元间的旋转测度（rotation measure）估算，探究分子云内磁场的性质及其时空变化。若此次探测得以确认，将为独立于传统解释框架的、难以直接测量的分子云磁场研究打开新窗口，从而为恒星形成与星际介质的物理机制研究提供关键阐释。