Asteroseismology of the Double-mode High-amplitude δ Scuti Star VX Hydrae

Xue, Hui-Fang; Fu, Jian-Ning; Fox-Machado, L.; Shi, Jian-Rong; Zhou, Yu-Tao; Zhang, Jun-Bo; Michel, R.; Yan, Hong-Liang; Niu, Jia-Shu; Zong, Wei-Kai; Su, Jie; Castro, A.; Ayala-Loera, C.; Altamirano-Dévora, L.
The Astrophysical Journal, Volume 861, Issue 2, article id. 96, 12 pp. (2018).


Bi-site time-series photometric and high-resolution spectroscopic observations were made for the double-mode high-amplitude δ Scuti star VX Hya. The fundamental frequency f 0 = 4.4763 c days‑1, the first overtone f 1 = 5.7897 c days‑1, and 23 harmonics and linear combinations of f0 and f 1 are detected by pulsation analysis. From the spectroscopic data, we get [Fe/H] = ‑0.2 ± 0.1 dex. The period change rate of the fundamental mode is obtained by using the Fourier-phase diagram method, which gives the value of (1/{P}0)({{dP}}0/{dt}) =(1.81+/- 0.09)× {10}-7{yr}}-1. With these results from the observations, we perform theoretical explorations with the stellar evolution code MESA, and constrain the models by fitting f 0, f 1, and (1/P 0)(dP 0/dt) within 3σ deviations. The results show that the period change of VX Hya could be ascribed to the evolutionary effect. The stellar parameters of VX Hya could be derived as: the mass 2.385 ± 0.025 M , the luminosity log(L/L ) = 1.93 ± 0.02, and the age (4.43 ± 0.13) × 108 years. VX Hya is found to locate at the post-main-sequence stage with a helium core and a hydrogen-burning shell on the H–R diagram.