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

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 . 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 3 σ 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) × 10 8 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.