Exploring the convective core of the high-amplitude δ Scuti star TIC 120857354 with asteroseismology

ABSTRACT Based on 2-min cadence TESS data, 20 confident independent frequencies were identified for the star TIC 120857354. The Kolmogorov–Smirnov test reveals a rotational splitting of 2.40 $\mu$Hz and a uniform frequency spacing of 74.6 $\mu$Hz. Subsequently, five sets of rotational splittings were discerned, including a quintuplet and four pairs of doublets, aligning with the characteristics of p-mode rotational splitting. Based on the sets of rotational splittings and the uniform frequency spacing, we finally identified four radial modes, six dipole modes, and 10 quadrupole modes. Furthermore, we found that the frequency separations within the $\ell$ = 2 sequences show a decreasing trend towards lower order modes, analogous to the $\ell$ = 0 sequences. A grid of theoretical models were computed to match the identified frequencies, revealing that TIC 120857354 is a main-sequence star with M = 1.54 $\pm$ 0.04 $\mathrm{M}_{\odot }$, Z = 0.015 $\pm$ 0.003, $T_{\rm eff}$ = 7441 $\pm$ 370 K, $\log g$ = 4.27 $\pm$ 0.01, R = 1.52 $\pm$ 0.01 $\mathrm{R}_{\odot }$, L = 6.33 $\pm$ 1.53 $\mathrm{L}_{\odot }$, age = 0.53 $\pm$ 0.07 Gyr, and $X_\mathrm{ c}/X_0$ = 0.84 $\pm$ 0.05. In-depth analyses suggest that $\ell$ = 2 may be p-dominated mixed modes with pronounced g-mode characteristics, enabling us to probe deeper into interiors of the star and determine the relative size of the convective core to be $R_\mathrm{ c}/R$ = 0.092 $\pm$ 0.002.