Parkes observations for project P1014 semester 2020OCTS_02

The spatial distribution of neutral gas is important for understanding the interstellar medium (ISM), its evolution, and star formation. However, the distribution of Tiny Scale Atomic Structures (TSAS), especially the extremely small scale structures with spatial scales ranging from sub to tens of AU is largely unexplored. The formation and evolution of TSAS are still unknown. Multi-epoch observations of HI absorption against pulsars are a tested, practical observational method to probe the TSAS. Based on our observations in the 2019APR, 2019OCT, and 2020APR semester, we successfully processed baseband data and detected the HI absorption variation towards PSR B1557-50 with spatial scales from 7 to 27 AU and significant dispersion measurements (DM) variations over several hours. In order to put a limit on the minimum size of TSAS we detected, meanwhile to reveal possible relation between magnetohydrodynamic turbulence and TSAS formation associated with DM variations, we propose four epoch observations towards PSR B1557-50. This will help us to better understand the role of turbulence and magnetic fields in the dynamics of interstellar gas, thus help reveal the origin of overdense and overpressured tiny scale atomic structures in the ISM.

中性气体的空间分布对于理解星际介质（interstellar medium, ISM）的特性、演化进程与恒星形成过程具有重要意义。然而，小尺度原子结构（Tiny Scale Atomic Structures, TSAS）——尤其是空间尺度介于亚天文单位至数十天文单位的极小型结构——的分布特征尚未得到充分探索，其形成与演化机制仍未明确。利用脉冲星背景下的中性氢吸收开展多历元观测，是一种经过验证且切实可行的探测TSAS的观测手段。基于我们在2019年春季、2019年秋季以及2020年春季观测学期获取的数据，我们已成功完成基带数据处理，并在脉冲星PSR B1557-50方向探测到尺度介于7至27天文单位的中性氢吸收变化，以及数小时尺度上的显著色散量（dispersion measurements, DM）变化。为限定本次探测到的TSAS的最小尺寸，同时揭示磁流体动力学湍流与伴随色散量变化的TSAS形成过程之间的潜在关联，我们提议针对PSR B1557-50开展四次历元观测。该观测计划将助力我们进一步明晰湍流与磁场在星际气体动力学中的作用，进而揭示星际介质中过密、过压小尺度原子结构的起源。