Kepler Discovery of GW Vir Pulsations of the Central Star of Planetary Nebula Kn 61

Abstract

We report the discovery of pulsations in the N-rich PG 1159-type central star of the planetary nebula Kn 61 based on one month of Kepler Short Cadence observations. We detect four significant peaks in the frequency range consistent with g-modes excited in GW Vir stars. From the detected modes, we identify a mean period spacing of $ΔΠ=21.526(6)$ s for a sequence of three $\ell=1$ modes. This allows us to derive the asteroseismic mass of the star, which we estimate to be $0.551(6)~\mathrm{M}_{\odot}$, consistent with the one derived from the evolutionary tracks. We also characterize sporadic brightening events in the Long Cadence Kepler light curve of Kn 61. If we assume these are caused by increases in effective temperature, we estimate their energies to be $\sim10^{40}$ erg, though this may not be accurate as the mechanism for releasing so much energy is still unknown.