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

Abstract

ABSTRACT EZ Cnc, or EPIC 212182292, is a non-Blažko RRab variable star located in the field of K2 Campaign 16. Its atmospheric parameters (Teff, 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 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, log g = 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.