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

EZ Cnc, or EPIC 212182292, is a non-Blako RRab variable star located in the field of K2 Campaign 16. Its atmospheric parameters (T-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 +/- 0.03M(circle dot), L = 42 +/- 2L(circle dot), T-eff = 6846 +/- 50K, logg = 2.79 +/- 0.01dex, 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.