TESS light curve of RU Lup from Sector 65 (2023). The light curve is plotted as a function of the time t from the beginning of the observation (MJD_beg = 60068.25). The top axis show the phase ϕ computed with P = 3.63 days (i.e., the spot period, Sec. 4.1). The reference date for ϕ = 0 is MJD₀ ≡ 59264.336. The blue lines mark the phase ϕ_S (from Sec. 4.1), where the maximum contribution from the hot spot is expected. The red lines mark the epochs of the CHIRON spectroscopic observations.