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

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Jiangtao Wang, Jianning Fu, Weikai Zong, Jiaxin Wang, Bo Zhang

EZ Cnc, or EPIC 212182292, is a non-Blazhko RRab variable star located in the field of K2 Campaign 16. Its atmospheric parameters (Teff, logg, [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 R21=0.5115(15),0.490(8), R31=0.3249(20),0.279(7) and Fourier phase differences φ21=2.7550(20),2.764(16), φ31=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±0.03 M⊙, L=42±2 L⊙, Teff=6846±50 K, logg=2.79±0.01 dex, and Z=0.006±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.

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