Asteroseismology of the High-amplitude $\delta$ Scuti Star EH Librae

Abstract

A subclass of intermediate mass variables $\delta$ Scuti stars, known as High-amplitude $\delta$ Scuti (HADS) stars, exhibits pronounced radial pulsations. We used ground- and space-based observations to perform an asteroseismic analysis of the HADS star EH Lib. Following the reduction of light curves, the frequency analysis reveals the dominant frequency as $f_0=11.3105{\mathrm{d}}^{-1}$ and two newly detected significant frequencies $f_1$ and $f_2$, in addition to the harmonics of $f_0$ and a linear combination. The period change rate is determined as $(1/P_0)(d{P}_0/dt)=(5.4\pm 0.5)\times 10^{-9}\mathrm{y}{\mathrm{r}}^{-1}$ derived from an O-C diagram, which is constructed from 342 times of maximum light spanning over 70 years. Using these observational constraints, along with the metallicities reported in the literature, we construct theoretical models using the stellar evolution code MESA and calculate the theoretical frequencies of the eigenmodes using the oscillation code GYRE. The appropriate models are selected by matching $f_0$, $(1/P_0)(d{P}_0/dt)$ and luminosity within their respective uncertainties. The results indicate that the observed period change of EH Lib can be attributed to stellar evolutionary effects. The stellar parameters of EH Lib are derived as: the mass of $1.555\pm 0.015M_{\odot }$, the luminosity of $\log (L/L_{\odot })=1.26\pm 0.02$, and the age of $(1.46\pm 0.05)\times 10^9\mathrm{years}$. EH Lib is classified as a single-radial-mode HADS star, located in the subgiant branch, with a helium core and hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables.

arXiv commentPublished in ApJ, 24 pages, 15 figures