Details of lpv during the trough event in TESS photometry. The top panel illustrates the variations of He I λ 5876, whilst the bottom panel displays those of Hα. The different colours correspond to different observations taken during the nights of 26–27 and 27–28 July 2021. The vertical panel on the right displays the TESS light curve. The colours of the symbols correspond to those used for the spectra.