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

Abstract

EZ Cnc, or EPIC 212182292, is a non-Blazhko RRab variable star located in the field of K2 Campaign 16. Its atmospheric parameters ($T_{\mathrm{eff}}$, $\log g$, [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 ${\phi }_{21}=2.7550(20),2.764(16)$, ${\phi }_{31}=5.7194(25),5.719(31)$ 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 $M=0.48\pm 0.03$ M${}_{\odot }$, $L=42\pm 2$ L${}_{\odot }$, $T_{\mathrm{eff}}=6846\pm 50$ K, $\log g=2.79\pm 0.01$ dex, and $Z=0.006\pm 0.002$, 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.

8 pages, 6 figures, 5 tables, Accepted for publication in MNRAS 9/6/2021

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• The Data Processing of the LAMOST Medium-Resolution Spectral Survey of Galactic Nebulae (LAMOST MRS-N Pipeline)
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