Asteroseismology of RRab variable star EZ Cnc from K2 photometry and LAMOST spectroscopy

TL;DR

This study combines K2 photometry and LAMOST spectroscopy to analyze the pulsation and atmospheric parameters of the RRab star EZ Cnc, deriving its fundamental properties and improving understanding of RR Lyrae period-luminosity relations.

Contribution

It provides the first detailed pulsation modeling of EZ Cnc using combined photometric and spectroscopic data, deriving precise stellar parameters and advancing RR Lyrae star characterization.

Findings

Derived fundamental frequency as 1.8323 d$^{-1}$ from K2 data.

Estimated stellar parameters: mass 0.48 M$_{igodot}$, luminosity 42 L$_{igodot}$, temperature 6846 K.

Identified four optimal pulsation models fitting the observed data.

Abstract

EZ Cnc, or EPIC 212182292, is a non-Blazhko RRab variable star located in the field of K2 Campaign 16. Its atmospheric parameters ($T_{\rm eff}$, $\log{g}$, [M/H]) and radial velocities are measured from the 55 high-quality LAMOST medium-resolution spectra. The fundamental frequency of pulsation is derived as $f=1.8323(17)$ d$^{-1}$ from the K2 light curves. The amplitude ratios $R_{21} = 0.5115(15), 0.490(8)$, $R_{31} = 0.3249(20), 0.279(7)$ and Fourier phase differences $\varphi_{21}=2.7550(20), 2.764(16)$, $\varphi_{31}=5.7194(25), 5.719(31)$ are determined from the Fourier decomposition of K2 light curve and LAMOST radial velocity curve, respectively. Through the constraints of the parameters, four optimal models are obtained in a time-dependent turbulent convection model survey for EPIC 212182292. The parameters of EPIC 212182292 are derived as $M=0.48\pm0.03$ M$_{\odot}$, $L = 42\pm2$ L$_{\odot}$, $T_{\rm eff}=6846\pm50$ K, $\log{g}=2.79\pm0.01$ dex, and $Z = 0.006\pm0.002$, respectively. The precisely determined parameters for RRab variable stars like EPIC 212180092 might help to better understand the period-luminosity relationship of RR Lyrae stars.