2024ApJ...976....2S

We investigated the pulsating behavior of TIC 400562821 using high-precision observations from TESS. Fourier analysis of time-series data revealed three independent frequencies. The period ratios of F to F1 (0.774) and F to F2 (0.625), along with an amplitude change of approximately 0.1 mag, indicate that TIC 400562821 is a triple-mode High-Amplitude δ Scuti (HADS) star. Using the Best Parent Method and the Γ_O functions, we identified that the harmonics and sum combination frequencies of F and F1 are caused by the nonlinear response of the stellar medium to pulsation. We also analyzed the amplitude variations of F, F1, and F2. Observational data over 76 days show stable amplitudes for these modes. However, Radial Stellar Pulsations modeling suggests that, over 10,000 cycles, the amplitude of F remains constant, while F1 gradually decreases and F2 approaches zero. This implies that TIC 400562821 may eventually evolve into a single-mode HADS star. Furthermore, asteroseismic modeling was performed, and several effects, such as the mixing-length parameter α_MLT and nonadiabatic, were examined on this star. In view of the results by Daszyńska-Daszkiewicz et al. (i.e., α_MLT < ∼1 for δ Scuti stars), TIC 400562821 is suggested to be more likely in the post-main-sequence stage, with mass M = 1.34-1.38 M_⊙ and metallicity Z = 0.007-0.008, but still warrants further study to ascertain its nature.