2018ApJ...861...96X

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 f₀ = 4.4763 c days^–1, the first overtone f₁ = 5.7897 c days^–1, and 23 harmonics and linear combinations of f₀ and f₁ 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/P₀)(dP₀/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 f₀, f₁, and (1/P₀)(dP₀/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) x 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.