Position of TIC 399725538 A (cyan cross) and B (pink cross) in the H-R diagram. The green solid line represents the zero-age main sequence, while the colored oblique solid and dashed lines indicate the instability strips of δ Sct and γ Dor stars, respectively (see J. W. Lee et al. 2024). The black solid lines denote the evolutionary sequences of ELM WDs with masses from 0.1611 M_⊙ to 0.2025 M_⊙, up to the first occurrence points of CNO flashes (L. G. Althaus et al. 2013). The dotted gray line shows the full evolutionary track of the 0.2025 M_⊙ model.