Parkes observations for project P1219 semester 2024APRS_02

The magnetic field potentially regulates the process of star formation and the evolution of molecular clouds. The Zeeman splitting measurement is the only method to estimate the magnetic field strength along the line of sight directly. The correlation between magnetic field strength and hydrogen column density provides a unique insight into discerning whether and where magnetic fields possess the strength to support gravitational contraction within clouds. Recent observations of OH absorption toward pulsars raise the possibility that the magnetic field strength estimates derived from Zeeman splitting in OH absorptions may be influenced by the angular sizes of background sources. We propose the continued monitoring of four pulsars exhibiting OH absorptions and observe two new pulsars located behind the molecular cloud regions where Zeeman detections of OH absorptions have been identified to constrain the magnetic field strength in quiescent molecular clouds with a characteristic spatial scale of several AUs for the first time, thus shedding light on the physics of star formation and the interstellar medium.

磁场可潜在调控恒星形成进程与分子云演化过程。塞曼分裂（Zeeman splitting）测量是唯一可直接沿视线方向估算磁场强度的方法。磁场强度与氢柱密度（hydrogen column density）之间的相关性，为辨析磁场是否具备足够强度以支撑云内引力坍缩（gravitational contraction）、以及该过程发生的具体位置，提供了独特的研究视角。近期针对脉冲星的羟基吸收（OH absorption）观测表明，基于羟基吸收谱塞曼分裂得到的磁场强度估算结果，或受背景源角尺寸的影响。我们提议对4颗已观测到羟基吸收的脉冲星开展持续监测，并对2颗位于已识别出羟基吸收塞曼探测结果的分子云区域后方的新脉冲星进行观测，以期首次对特征空间尺度为数个天文单位（AU）的宁静分子云的磁场强度进行约束，从而阐明恒星形成与星际介质（interstellar medium）的物理机制。