Discovery and Characterization of Three New High-amplitude <i>δ</i> Scuti Stars from TESS Observations

Abstract We report the discovery and detailed analysis of three new high-amplitude δ Scuti (HADS) stars, TIC 408074920, TIC 189714989, and TIC 34137913, identified from Transiting Exoplanet Survey Satellite short-cadence observations. Fourier analysis reveals dominant radial modes accompanied by rich harmonic structures in all three stars, confirming their HADS classification. In addition, TIC 189714989 exhibits clear symmetric side peaks around the radial harmonics, indicative of amplitude and/or phase modulation. Broadband spectral energy distribution (SED) fitting constrained by Gaia DR3 parallaxes provides independent estimates of the stellar effective temperatures and radii. These are compared with results from stellar evolutionary and seismic modeling based on MESA and GYRE . For two targets, the SED-derived and seismic radii are mutually consistent, while TIC 408074920 displays a significant discrepancy, plausibly attributable to the different sensitivities of the two methods and additional systematic effects. These findings highlight the diversity of amplitude variability among classical HADS and emphasize the importance of the long-term monitoring that future missions such as PLATO will allow in order to explore the underlying physical mechanisms of this variability.