2018ApJ...866...59T

We present an asteroseismic analysis of the Kepler light curve of KIC 8263801, a red-giant star in the open cluster NGC 6866 that has previously been reported to be a helium-burning red-clump (RC) star. We extracted the frequencies of the radial and quadrupole modes from its frequency power spectrum and determined its properties using a grid of evolutionary models constructed with MESA. The oscillation frequencies were calculated using the GYRE code and the surface term was corrected using the Ball & Gizon prescription. We find that the star has a mass of M/M_☉ = 1.793 ± 0.072, age t = 1.48 ± 0.21 Gyr, and radius R/R_☉ = 10.53 ± 0.28. By analyzing the internal structure of the best-fitting model, we infer the evolutionary status of the star KIC 8263801 as being on the ascending part of the red-giant branch, and not on the RC. This result is verified using a purely asteroseismic diagnostic, the ε_c - Δν_c diagram which can distinguish red-giant branch stars from red-clump stars. Finally, by comparing its age with NGC 6866 (t = 0.65 ± 0.1 Gyr), we conclude that KIC 8263801 is not a member of this open cluster.