Asteroseismology of the Double-mode High-amplitude δ Scuti Star VX Hydrae
Fu, Jian-Ning; Su, Jie; Castro, A.; Yan, Hong-Liang; Shi, Jian-Rong; Zhou, Yu-Tao; Fox-Machado, L.; Xue, Hui-Fang; Niu, Jia-Shu; Michel, R.; Zhang, Jun-Bo; Zong, Wei-Kai; Ayala-Loera, C.; Altamirano-Dévora, L.
China, México, United Kingdom
Abstract
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 f 0 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.