Parkes observations for project P1014 semester 2020OCTS_03

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.