Parkes observations for project P1219 semester 2025APRS_01

Magnetic fields are fundamental in regulating star formation and the evolution of molecular clouds. Zeeman splitting offers a unique method to directly measure line-of-sight magnetic field strengths in interstellar environments, from the diffuse ISM to dense cores. Observations of HI and OH absorption toward pulsars provide an unprecedented opportunity to measure magnetic fields with high precision, benefiting from pulsars' small angular sizes and reliable Stokes V spectra unaffected by instrumental effects. Our recent tentative Zeeman splitting detections in OH absorption toward PSR J1644-4559 with Parkes reveal magnetic field strengths that suggest magnetically subcritical states, where magnetic pressure counteracts gravity. This challenges conventional theories of subcritical cold neutral medium (CNM) transitioning to supercritical star-forming molecular clouds, emphasizing the need for detailed investigation. We propose a continuation of Zeeman splitting studies through high-sensitivity OH and HI absorption observations of pulsars PSR J1644-4559, J1721-3532, and J1852+0031 using Parkes. By employing an innovative phase-resolved spectral technique and extending integration times, we aim to enhance Zeeman detection sensitivity and study magnetic field transitions in the CNM and quiescent molecular clouds. This work will refine our understanding of subcritical-to-supercritical transitions in star formation, establish pulsar absorption as a robust probe of interstellar magnetic fields, and advance observational techniques critical to star formation studies.

磁场是调控恒星形成与分子云演化的核心物理要素。塞曼分裂（Zeeman splitting）是一种可直接测量星际环境视向磁场强度的独特方法，适用范围覆盖从弥漫星际介质到致密核区的各类星际介质。针对脉冲星的HI与OH吸收观测，得益于脉冲星极小的角尺度以及不受仪器效应干扰的可靠斯托克斯V谱，为高精度测量磁场提供了前所未有的契机。我们利用帕克斯（Parkes）望远镜对脉冲星PSR J1644-4559的OH吸收谱开展观测，首次得到试探性的塞曼分裂探测结果，其测得的磁场强度表明该天体处于磁亚临界状态——即磁压与引力相互抗衡的状态。该发现对冷中性介质（CNM, Cold Neutral Medium）从亚临界态向形成恒星的超临界分子云过渡的传统理论构成挑战，凸显了开展深入系统性研究的必要性。我们提出后续研究计划：利用帕克斯（Parkes）望远镜，对PSR J1644-4559、PSR J1721-3532与PSR J1852+0031三颗脉冲星开展高灵敏度的OH与HI吸收观测，延续塞曼分裂相关研究。通过采用创新性的相位分辨光谱技术并延长积分时长，我们旨在提升塞曼分裂的探测灵敏度，进而研究冷中性介质与宁静分子云中的磁场跃迁过程。本研究将深化我们对恒星形成过程中亚临界到超临界态跃迁的认知，确立脉冲星吸收观测作为星际磁场可靠探针的地位，并推动恒星形成研究所需的关键观测技术发展。